Process for the preparation of unsaturated carboxylic acids by carbonylation of allyl alcohols and their acylation products

ABSTRACT

The present invention relates to a process for carbonylating allyl alcohols at low temperature, low pressure and/or low catalyst loading. In an alternative embodiment, an acylation product of the allyl alcohol is used for the carbonylation. The present invention likewise relates to the preparation of conversion products of these carbonylation products and specifically of (−)-ambrox.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage application (under 35 U.S.C. § 371) of PCT/EP2018/053535, filed Feb. 13, 2018, which claims benefit of European Application No. 17157950.1, filed Feb. 24, 2017, both of which are incorporated herein by reference in their entirety.

SEQUENCE LISTING

The instant application contains a Sequence Listing which has been submitted electronically in ASCII format and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Jan. 28, 2021, 2021, is named 074012-0409-US-592346-SL.txt and is 64,063 bytes in size.

BACKGROUND OF THE INVENTION

The present invention relates to a process for carbonylating allyl alcohols at low temperature, low pressure and/or low catalyst loading. In an alternative embodiment, an acylation product of the allyl alcohol is used for the carbonylation. The present invention also relates to the preparation of conversion products of these carbonylation products and specifically of (−)-ambrox.

STATE OF THE ART

The carbonylation products of allyl alcohols are valuable intermediates for preparation of a multitude of commercial products. By carbonylation of the allyl alcohols nerolidol and farnesol, it is possible, for example, to obtain carboxylic acids which, after reduction to the corresponding alcohols, can be cyclized to give valuable aroma chemicals. For example, (3E,7E)-homofarnesylic acid from the carbonylation of E-nerolidol can be subjected to a reduction to obtain (3E,7E)-homofarnesol

and the latter can be further subjected to a cyclization to obtain (−)-ambrox

Processes for carbonylation of allyl alcohols to give their C1-extended linear carboxylic acids or carboxylic esters in the presence of homogeneous and also heterogeneous catalysts are known from the literature. However, these processes are economically disadvantageous for various reasons. For example, it is known that the direct carbonylation of allyl alcohols requires harsh conditions with regard to temperature and pressure and high catalyst loadings; in most cases, moreover, high conversions are achievable at all only with addition of halide-containing additives even when high pressures or temperatures or catalyst loadings are used. There is therefore a need for a process which enables the economically advantageous preparation of the carbonylation products of allyl alcohols.

Bertleff, W., Roeper, M. and Sava X. 2007 in Ullmann's Encyclopedia of Industrial Chemistry, Vol. 7, pages 74-98, 2012, Wiley-VCH describe carbonylation methods of industrial relevance.

Tsuji et al. in J. Am. Chem. Soc. 86, 1964, 4350-4353 describe the catalytic carbonylation of allyl compounds using palladium(II)chloride. Specifically, allyl chloride, allyl alcohol and analogous compounds are reacted with CO in organic solvents, giving the corresponding carboxylic esters with ethanol. The 3-butenoic anhydride is obtained from allyl alcohol in benzene as the solvent. The amount of palladium chloride used, based on allyl compound, is more than 5 mol % at pressures of 100 to 150 bar and temperatures of greater than 80° C.

B. Gabriele et al. in the Journal of Molecular Catalysis A, 111, 1996, 43-48 describe the carbonylation of allyl alcohols to give unsaturated acids or esters. The conversion is effected in dimethylacetamide or methanol/dimethylacetamide mixtures at pressures of 50-100 bar and temperatures of greater than 80° C. using a Pd catalyst at loadings of 2 mol % to 4 mol %.

T. Mandai in a review article in the Handbook of Organopalladium Chemistry for Organic Synthesis, editor: E. Negishi, Wiley-VCH, New York, Vol. 2, 2002, 2505-2517, describes, inter alfa, the carbonylation of allyl compounds with homogeneous palladium catalysts. It is pointed out that the carbonylation of allylic alcohols requires severe reaction conditions. It is likewise stated that the carbonylation of acetylated allyl alcohols, such as the structurally isomeric compounds (A) and (B), is generally difficult. According to the teaching of this document, however, the conversion succeeds in the presence of catalytic amounts of NaBr.

ACS Catal., 4, 2014, 2977-2989, in a review article, likewise describes the carbonylation of allyl compounds with homogeneous palladium catalysts.

By the process as described in the literature, the direct carbonylation of allyl alcohols requires high pressures or temperatures or catalyst loadings or the addition of halides as additive, and usually even a combination of at least two of these conversion-enhancing measures, in order to achieve sufficiently high reaction rates.

For instance, U.S. Pat. No. 4,801,743 describes the carbonylation of allyl alcohol (2-propen-1-ol) using a heterogeneous Pd catalyst in the absence of water and in the presence of a catalytically active amount of a hydrogen halide selected from HF, HCl, HBr and HI at pressures of greater than 150 bar and temperatures of greater than 80° C.

EP 0428979 A2 describes the carbonylation of allylic butenols and butenol esters using a homogeneous Rh catalyst in the presence of HBr or HI at CO pressures of 1 to 200 bar and temperatures of 10 to 250° C.

The aforementioned documents do describe processes for carbonylation of allyl alcohols to give their C1-extended linear carboxylic acids or carboxylic esters. What is not described, however, is the carbonylation of allyl alcohols having terpene-like hydrocarbyl radicals and specifically the carbonylation of linalool to give E/Z-4,8-dimethyl-3,7-nonadienoic acid and of E-nerolidol or farnesol to give E/Z-homofarnesylic acid. All the processes described in the aforementioned documents also have one or more disadvantages that make them seem unsuitable for use for said conversions. For instance, the catalysts described in the aforementioned documents have too low an activity or the processes entail excessively harsh reaction conditions (with regard to acid, CO pressure, temperature) in order to enable effective economic carbonylation of allyl alcohols overall, and specifically the allyl alcohols having terpene-like hydrocarbyl radicals mentioned.

For instance, processes that necessitate high-pressure operation are industrially very costly. In many of the processes mentioned, the amount of catalyst used based on the substrate to be carbonylated is also very high. In the case of use of homogeneous catalyst systems that are generally discharged together with the product, high costs thus arise as a result of the catalyst recycling and unavoidable catalyst losses. Also problematic is the use of added hydrohalic acids and salts thereof. Because of the high corrosivity of these compounds, the use of reactors made from particularly high-quality steels is required. Moreover, process conditions of this kind are unsuitable for the conversion of E-nerolidol to homofarnesylic acid, since E-nerolidol does not have adequate stability toward strong acids such as HI.

Processes for carbonylation of E-nerolidol in the presence of homogeneous catalysts to give homofarnesylic acid or homofarnesylic acid alkyl esters are known in principle.

WO 92/06063 describes a process for preparing unsaturated carboxylic acids by carbonylating the corresponding allylic alcohols, for example the carbonylation of (E)-nerolidol with addition of catalytic amounts of palladium(II) chloride.

What is also described is the reduction of the carbonylation product thus obtained to give homofarnesol or monocyclohomofarnesol and the acid-catalyzed cyclization of homofarnesol to obtain 3a,6,6,9a-tetramethyldodecahydronaphtho-[2,1-b]-furan, an ambergris-like fragrance. A disadvantage of this process is that the carbonylation reaction takes place at high CO pressures of about 70 bar. In addition, a high catalyst loading of 0.6 mol % is used.

EP 0146859 A2 describes a process for preparing 4-substituted but-3-ene-1-carboxylic acids and esters thereof by carbonylation in the presence or absence of a lower alkanol (specifically methanol) with complexes of a palladium halide and a tertiary organic phosphine. The conversion is effected at pressures of 200 to 700 bar and temperatures of 50 to 150° C.

It is also known that substitutes for CO that enable ambient pressure conversion can be used for carbonylation. WO 2015/061764 and Tetrahedron: Asymmetry, 20, 2009, 1637-1640 describe the Pd-catalyzed use of N,N-dimethylformamide dimethyl acetal (DMFDMA) as CO substitute in the conversion of E-nerolidol and subsequent hydrolysis in methanol to give homofarnesylic acid methyl ester. However, such a two-stage process is synthetically complex and is also costly owing to the CO substitutes used, and so it is uneconomic on an industrial scale for carbonylation of allyl alcohols.

It is also known that allyl alcohols can be converted to the corresponding acetates and these acetates can be used as substrates in carbonylation reactions under comparatively mild conditions (pressures, for example, of 30 bar below 100° C.).

JOC, 53 1988, 3832-3828 describes the Pd- or Pt-catalyzed cyclizing carbonylation of cinnamyl acetates to 1-naphthol derivatives. The reaction is effected in the presence of acetic anhydride and triethylamine at 160° C. and 60 bar CO. The reason given for the addition of acetic anhydride is the necessity of converting the 1-naphthol formed as an intermediate to the corresponding acetate, since free 1-naphthol would inhibit the cyclocarbonylation. In terms of type, this reaction is a carbonylation in the presence of Pd and acetic anhydride, but does not lead to carboxylic acid derivatives.

Tetrahedron Letters, 29, 1988, 4945-4948 describes the conversion of allyl acetates in ethanol to the corresponding C1-extended carboxylic esters. The conversions are effected at 30 to 80 bar CO and 50 to 80° C. However, the conversion is effected not just in the presence of a base but also of catalytic amounts of bromide ions, which is said to dramatically accelerate the reaction. This document additionally points out that poor results were achieved with Pd(II) catalysts such as palladium(II) acetate (Pd(OAc)₂).

JOC, 58, 1993, 1538-1545 describes the Pd(0)-catalyzed alkoxycarbonylation of allyl acetates. This document too refers to the necessity of the presence of halide ions for acceleration of the reaction. By contrast, only a low reactivity in the carbonylation is ascribed to the allyl acetates.

There is thus no specific method in the literature for direct carbonylation of allyl alcohols and specifically of E-nerolidol to give homofarnesylic acid (or derivatives of homofarnesylic acid such as the corresponding salts or esters) that proceeds effectively and economically under mild reaction conditions. This is understood to mean that the conversion proceeds at pressures in the region of not more than 30 bar CO and/or at temperatures below 100° C. and/or in the absence of halogen compounds selected from hydrohalic acids and alkali metal, alkaline earth metal or ammonium halides or a combination of at least two of these measures.

It has been found that, surprisingly, even the addition of catalytic amounts of a carboxylic anhydride, such as Ac₂O (acetic anhydride) is sufficient to fully carbonylate allyl alcohols under mild reaction conditions and with low catalyst loadings to the corresponding carboxylic acid. Particularly advantageous results are achieved here with addition of a nucleophilic reagent such as an alkylpyridine, 4-(1-pyrrolidinyl)pyridine or a dialkylaminopyridine, specifically DMAP (4-dimethylaminopyridine). Particularly surprisingly, even the addition of catalytic amounts of acylation products of allyl alcohols without the addition of carboxylic anhydrides is sufficient to accelerate the reaction by a number of orders of magnitude. These acylation products of allyl alcohols may also be esters of allyl alcohols other than the substrate itself with carboxylic acids (for example allyl acetate). In the light of the prior art, the person skilled in the art, if considering the use of acylation products of allyl alcohol at all, would have used at least a stoichiometric amount of acylated allyl alcohol (or of an acylating agent). The fact that this reaction regime works as described with catalytic amounts of activating reagent was unknown, was not obvious and is very advantageous for the efficiency of the overall process.

It is therefore an object of the present invention to provide a process for carbonylating allyl alcohols or the acylation products thereof to obtain unsaturated carboxylic acids or salts thereof, in which the aforementioned disadvantages are avoided.

In a specific embodiment, it is an object of the invention to provide a process for carbonylating E-nerolidol in which a product mixture comprising (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid (homofarnesylic acid) and (3Z,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid or the salts thereof is obtained.

It has now been found that, surprisingly, the carbonylation of allyl alcohols and derivatives of allyl alcohol to give C1-extended unsaturated carboxylic acids or corresponding carboxylic salts can be conducted at temperatures of not more than 100° C. It has been found that, advantageously, the carbonylation of alcohols and derivatives of allyl alcohol to give C1-extended unsaturated carboxylic acids or corresponding carboxylic salts can be conducted at temperatures of not more than 100° C. and at low pressure, for example at a pressure of not more than 30 bar. It has additionally been found that, advantageously, the carbonylation of alcohols and derivatives of allyl alcohol to give C1-extended unsaturated carboxylic acids or corresponding carboxylic salts can be conducted at temperatures of not more than 100° C. with simultaneously low catalyst loadings of less than 0.3 mol % and at simultaneously low pressure, for example at a pressure of not more than 30 bar. It has additionally been found that the conversion can also be effected without addition of accelerating halides.

SUMMARY OF THE INVENTION

The invention firstly provides a process for preparing a composition comprising at least one unsaturated carboxylic acid of the general formula (I)

or a salt thereof, in which

-   R¹ is hydrogen, linear or branched C₁-C₂₄-alkyl, linear or branched     C₂-C₂₄-alkenyl having 1, 2, 3 or more than 3 C—C double bonds,     unsubstituted C₅-C₁₂-cycloalkyl or C₅-C₁₂-cycloalkyl substituted by     1, 2 or 3 C₁-C₆-alkyl radicals or unsubstituted aryl or aryl     substituted by 1, 2 or 3 C₁-C₆-alkyl radicals, -   R² is hydrogen, linear or branched C₁-C₂₄-alkyl or linear or     branched C₂-C₂₄-alkenyl having 1, 2, 3 or more than 3 C—C double     bonds, or -   R¹ and R² together with the carbon atom to which they are bonded are     unsubstituted C₅-C₇-cycloalkyl or are C₅-C₇-cycloalkyl bearing 1, 2     or 3 linear or branched C₁-C₆-alkyl radicals,     in which an allyl alcohol selected from compounds of the general     formulae (II.1) and (II.2)

is subjected to a carbonylation by reaction with carbon monoxide in the presence of a transition metal catalyst comprising at least one metal of groups 8, 9 and 10 of the Periodic Table of the Elements, wherein the reaction is additionally effected in the presence of at least one organic phosphorus compound as ligand and in the presence of a substoichiometric amount, based on the allyl alcohol, of a compound A) selected from anhydrides of aliphatic C₁-C₁₂-monocarboxylic acids, anhydrides of aliphatic C₄-C₂₀-dicarboxylic acids, anhydrides of cycloaliphatic C₇-C₂₀-dicarboxylic acids, anhydrides of aromatic C₈-C₂₀-dicarboxylic acids and acylated allyl alcohols of the formulae (III.1) and (III.2)

in which

-   R³ is hydrogen, linear or branched C₁-C₂₄-alkyl, linear or branched     C₂-C₂₄-alkenyl having 1, 2, 3 or more than 3 C—C double bonds,     unsubstituted C₅-C₁₂-cycloalkyl or C₅-C₁₂-cycloalkyl substituted by     1, 2 or 3 C₁-C₆-alkyl radicals or unsubstituted aryl or aryl     substituted by 1, 2 or 3 C₁-C₆-alkyl radicals, -   R⁴ is hydrogen, linear or branched C₁-C₂₄-alkyl or linear or     branched C₂-C₂₄-alkenyl having 1, 2, 3 or more than 3 C—C double     bonds, or -   R³ and R⁴ together with the carbon atom to which they are bonded are     unsubstituted C₅-C₇-cycloalkyl or are C₅-C₇-cycloalkyl bearing 1, 2     or 3 linear or branched C₁-C₆-alkyl radicals, R⁵ is C₁-C₅-alkyl,     and wherein the reaction is effected at a temperature of not more     than 100° C.

The embodiment of the process of the invention in which an allyl alcohol selected from compounds of the general formulae (II.1) and (II.2) is used in the presence of a compound A) for the reaction is also referred to hereinafter as “Variant 1”.

A specific embodiment of variant 1 is a process for preparing a composition comprising at least one unsaturated carboxylic acid of the general formula (I)

or of a salt thereof, in which

-   R¹ is hydrogen, linear or branched C₁-C₂₄-alkyl, linear or branched     C₂-C₂₄-alkenyl having 1, 2, 3 or more than 3 C—C double bonds,     unsubstituted C₅-C₁₂-cycloalkyl or C₅-C₁₂-cycloalkyl substituted by     1, 2 or 3 C₁-C₆-alkyl radicals or unsubstituted aryl or aryl     substituted by 1, 2 or 3 C₁-C₆-alkyl radicals, -   R² is hydrogen, linear or branched C₁-C₂₄-alkyl or linear or     branched C₂-C₂₄-alkenyl having 1, 2, 3 or more than 3 C—C double     bonds, or -   R¹ and R² together with the carbon atom to which they are bonded are     unsubstituted C₅-C₇-cycloalkyl or are C₅-C₇-cycloalkyl bearing 1, 2     or 3 linear or branched C₁-C₆-alkyl radicals,     in which an allyl alcohol selected from compounds of the general     formulae (II.1) and (II.2)

is subjected to a carbonylation by reaction with carbon monoxide in the presence of a transition metal catalyst comprising at least one metal of groups 8, 9 and 10 of the Periodic Table of the Elements, wherein the reaction is additionally effected in the presence of at least one organic phosphorus compound as ligand and in the presence of a substoichiometric amount, based on the allyl alcohol, of a compound A) selected from anhydrides of aliphatic C₁-C₁₂-monocarboxylic acids, anhydrides of aliphatic C₄-C₂₀-dicarboxylic acids, anhydrides of cycloaliphatic C₇-C₂₀-dicarboxylic acids, anhydrides of aromatic C₈-C₂₀-dicarboxylic acids and acylated allyl alcohols of the formulae (III.1) and (III.2)

in which

-   R³ is hydrogen, linear or branched C₁-C₂₄-alkyl, linear or branched     C₂-C₂₄-alkenyl having 1, 2, 3 or more than 3 C—C double bonds,     unsubstituted C₅-C₁₂-cycloalkyl or C₅-C₁₂-cycloalkyl substituted by     1, 2 or 3 C₁-C₆-alkyl radicals or unsubstituted aryl or aryl     substituted by 1, 2 or 3 C₁-C₆-alkyl radicals, -   R⁴ is hydrogen, linear or branched C₁-C₂₄-alkyl or linear or     branched C₂-C₂₄-alkenyl having 1, 2, 3 or more than 3 C—C double     bonds, or -   R³ and R⁴ together with the carbon atom to which they are bonded are     unsubstituted C₅-C₇-cycloalkyl or are C₅-C₇-cycloalkyl bearing 1, 2     or 3 linear or branched C₁-C₆-alkyl radicals, -   R⁵ is C₁-C₅-alkyl,     and wherein the reaction is effected at a temperature of not more     than 100° C. and at a pressure of not more than 30 bar.

In an alternative embodiment, it is possible to use an acylated allyl alcohol for the carbonylation. In this variant too, it is possible to conduct the reaction under advantageously mild reaction conditions. According to the invention, the conversion in this variant is effected in the presence of water. The invention therefore further provides a process for preparing a composition comprising at least one unsaturated carboxylic acid of the general formula (I)

or of a salt thereof, in which

-   R¹ is hydrogen, linear or branched C₁-C₂₄-alkyl, linear or branched     C₂-C₂₄-alkenyl having 1, 2, 3 or more than 3 C—C double bonds,     unsubstituted C₅-C₁₂-cycloalkyl or C₅-C₁₂-cycloalkyl substituted by     1, 2 or 3 C₁-C₆-alkyl radicals or unsubstituted aryl or aryl     substituted by 1, 2 or 3 C₁-C₆-alkyl radicals, -   R² is hydrogen, linear or branched C₁-C₂₄-alkyl or linear or     branched C₂-C₂₄-alkenyl having 1, 2, 3 or more than 3 C—C double     bonds, or -   R¹ and R² together with the carbon atom to which they are bonded are     unsubstituted C₅-C₇-cycloalkyl or are C₅-C₇-cycloalkyl bearing 1, 2     or 3 linear or branched C₁-C₆-alkyl radicals,     in which an acylated allyl alcohol selected from compounds of the     general formulae (IV. 1) and (IV.2)

in which R⁶ is C₁-C₅-alkyl, is subjected to a carbonylation by reaction with carbon monoxide in the presence of a transition metal catalyst comprising at least one metal of groups 8, 9 and 10 of the Periodic Table of the Elements, wherein the reaction is additionally effected in the presence of at least one organic phosphorus compound as ligand and in the presence of water and wherein the reaction is effected at a temperature of not more than 100° C.

The embodiment of the process of the invention in which an acylated allyl alcohol selected from compounds of the general formulae (IV.1) and (IV.2) is used for the reaction is also referred to hereinafter as “Variant 2”.

A specific embodiment of variant 2 is a process for preparing a composition comprising at least one unsaturated carboxylic acid of the general formula (I)

or of a salt thereof, in which

-   R¹ is hydrogen, linear or branched C₁-C₂₄-alkyl, linear or branched     C₂-C₂₄-alkenyl having 1, 2, 3 or more than 3 C—C double bonds,     unsubstituted C₅-C₁₂-cycloalkyl or C₅-C₁₂-cycloalkyl substituted by     1, 2 or 3 C₁-C₆-alkyl radicals or unsubstituted aryl or aryl     substituted by 1, 2 or 3 C₁-C₆-alkyl radicals, -   R² is hydrogen, linear or branched C₁-C₂₄-alkyl or linear or     branched C₂-C₂₄-alkenyl having 1, 2, 3 or more than 3 C—C double     bonds, or -   R¹ and R² together with the carbon atom to which they are bonded are     unsubstituted C₅-C₇-cycloalkyl or are C₅-C₇-cycloalkyl bearing 1, 2     or 3 linear or branched C₁-C₆-alkyl radicals,     in which an acylated allyl alcohol selected from compounds of the     general formulae (IV.1) and (IV.2)

in which R⁶ is C₁-C₅-alkyl, is subjected to a carbonylation by reaction with carbon monoxide in the presence of a transition metal catalyst comprising at least one metal of groups 8, 9 and 10 of the Periodic Table of the Elements, wherein the reaction is additionally effected in the presence of at least one organic phosphorus compound as ligand and in the presence of water and wherein the reaction is effected at a temperature of not more than 100° C. and at a pressure of not more than 30 bar.

A further alternative embodiment relates to processes for preparing a composition comprising at least one unsaturated carboxylic acid of the general formula (I)

or a salt thereof, in which

-   R¹ is hydrogen, linear or branched C₁-C₂₄-alkyl, linear or branched     C₂-C₂₄-alkenyl having 1, 2, 3 or more than 3 C—C double bonds,     unsubstituted C₅-C₁₂-cycloalkyl or C₅-C₁₂-cycloalkyl substituted by     1, 2 or 3 C₁-C₆-alkyl radicals or unsubstituted aryl or aryl     substituted by 1, 2 or 3 C₁-C₆-alkyl radicals, -   R² is hydrogen, linear or branched C₁-C₂₄-alkyl or linear or     branched C₂-C₂₄-alkenyl having 1, 2, 3 or more than 3 C—C double     bonds, or -   R¹ and R² together with the carbon atom to which they are bonded are     unsubstituted C₅-C₇-cycloalkyl or are C₅-C₇-cycloalkyl bearing 1, 2     or 3 linear or branched C₁-C₆-alkyl radicals,     in which an allyl alcohol selected from compounds of the general     formulae (II.1) and (II.2)

is subjected to a carbonylation by reaction with carbon monoxide in the presence of a transition metal catalyst comprising at least one metal of groups 8, 9 and 10 of the Periodic Table of the Elements, wherein the reaction is additionally effected in the presence of at least one organic phosphorus compound as ligand and in the presence of a substoichiometric amount, based on the allyl alcohol, of a compound B)

in which

-   R¹⁰ and R¹¹, independently of one another, are C₁-C₆-alkyl,     C₁-C₆-fluoroalkyl or phenyl which is unsubstituted or substituted by     a substituent selected from bromo, nitro and C₁-C₄-alkyl;     and wherein the reaction is effected at a temperature of not more     than 100° C. Specifically, the reaction is effected at a temperature     of not more than 100° C. and a pressure of not more than 30 bar.

In this variant too, it is possible to conduct the reaction under advantageously mild reaction conditions. The embodiment of the process of the invention in which an allyl alcohol selected from compounds of the general formulae (II.1) and (II.2) is used for reaction in the presence of a compound B) is also referred to hereinafter as “variant 3”.

The invention further provides a process for preparing (−)-ambrox (VIII)

in which

-   a1) a mixture of (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic     acid and (3Z,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid     obtainable by a process as defined above is provided; -   b1) the mixture of (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic     acid and (3Z,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid is     subjected to a separation to obtain     (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid; -   c1) the (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid is     subjected to a reduction to obtain (3E,7E)-homofarnesol (VI); -   d1) the (3E,7E)-homofarnesol (VI) is subjected to a cyclization to     obtain (−)-ambrox (VIII);     or -   a2) a mixture of (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic     acid and (3Z,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid     obtainable by a process as defined above is provided; -   b2) the mixture of (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic     acid and (3Z,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid is     subjected to a separation to obtain     (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid; -   c2) the (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid is     subjected to a cyclization to obtain sclareolide (VII); -   d2) the sclareolide (VII) is subjected to a reduction to obtain     (−)-ambrox (VIII).

DESCRIPTION OF THE INVENTION

The processes of the invention for preparing a composition comprising at least one unsaturated carboxylic acid of the general formula (I) have the following advantages:

-   -   Variant 1 of the process enables the effective and economic         conversion of allyl alcohols to their C1-extended unsaturated         carboxylic acids or corresponding carboxylic salts. Much milder         reaction conditions (with simultaneously very low catalyst         loadings) are possible here than in the processes known from the         prior art. Specifically, conversion is possible at lower         temperature and/or a lower pressure and/or a lower catalyst         loading than in the known processes.     -   It is particularly advantageous that, in variant 1 of the         process of the invention, conversion in the presence of         catalytic (i.e. substoichiometric) amounts of anhydride is         sufficient to fully carbonylate the allylic alcohols under mild         reaction conditions and at low catalyst loadings to the         corresponding carboxylic acids. Particularly surprisingly, even         the addition of catalytic amounts of other anhydride formers,         such as allyl acetate (propenyl acetate) or different acylation         products of allyl alcohols is sufficient to distinctly         accelerate the reaction. The addition of additional anhydride is         not required here. Without wishing to be bound to any theory, it         is assumed that this is attributable to the fact that, under the         reaction conditions, there is initial carbonylation of the         acylated allyl alcohol added (e.g. allyl acetate CH₂═CHCH₂OAc)         to give an anhydride intermediate (e.g. CH₂═CHCH₂C(O)OAc), and         the anhydride formed in situ activates the allylic alcohol used         (e.g. nerolidol) with elimination of carboxylic acid (e.g.         CH₂═CHCH₂CO₂H), simultaneously generating new acylated allyl         alcohol (e.g. nerolidyl acetate) which can in turn be         carbonylated again to give the corresponding anhydride         intermediate (mixed anhydride of acetic acid and homofarnesylic         acid).     -   The possibility of using catalytic amounts of a nucleophilic         reagent in variant 1 of the process is very advantageous for the         efficiency of the overall process.     -   The process of the invention according to variant 1 enables the         carbonylation of allyl alcohols to obtain the corresponding         carboxylic acids or carboxylic salts in a single reaction stage,         i.e. without the isolation of an intermediate. For example, it         is unnecessary to activate the allyl alcohol used in a first         reaction step using stoichiometric amounts of acylating agent.     -   If the allyl alcohols used for carbonylation comprise further         internal double bonds, these are essentially neither         carbonylated nor isomerized.     -   The alternative variant 2 of the process is based on the         carbonylation of acylated alcohols to give their C1-extended         unsaturated carboxylic acids in the presence of water under mild         reaction conditions.     -   The processes according to variants 1 and 2 make it possible to         dispense with the use of added hydrohalic acids and salts         thereof.     -   The process according to variant 1 specifically enables the         carbonylation of allyl alcohols having terpene-like hydrocarbyl         radicals and specifically the carbonylation of linalool to give         E/Z-4,8-dimethyl-3,7-nonadienoic acid and of E-nerolidol or         farnesol to give E/Z-homofarnesylic acid under mild reaction         conditions.     -   By the process according to variant 1, it is advantageously         possible to carbonylate E-nerolidol to obtain a reaction mixture         composed of (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid         (homofarnesylic acid) and         (3Z,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid or the         salts thereof.

In the compounds of the general formulae (I), (II.2), (III.2) and (IV.2)

the wavy bond is supposed to indicate that the compound may be the pure Z isomer, the pure E isomer or any E/Z mixture. It will be self-evident to the person skilled in the art that, in the compounds of the general formulae (I), (II.2), and (IV.2), E and Z isomers can only exist when two different substituents R¹ and R² are bonded to the double bond. In the compounds of the general formula (III.2), E and Z isomers may exist only when two different substituents R³ and R⁴ are bonded to the double bond. The stereochemical configuration at the double bond is ascertained with the aid of the Cahn-Ingold-Prelog rules (see E/Z notation, en.wikipedia.org/wiki/E-Z_notation).

In the context of the present invention, the E/Z mixture of the general formula (I) is also referred to as E/Z acid mixture of the formula (I). In the E/Z acid mixture of the general formula (I), R¹ and R² have different meanings. The E/Z acid mixture of the formula (I) comprises the 3-(E) isomer of the unsaturated carboxylic acid of the formula I and the 3-(Z) isomer of the unsaturated carboxylic acid of the formula I. The 3-(E) isomer of the unsaturated carboxylic acid of the formula I is referred to hereinafter as 3-(E) isomer of the formula (I-E), and the 3-(Z) isomer of the unsaturated carboxylic acid as the 3-(Z) isomer of the formula (I-Z).

In the general formulae of the compounds I-Z and I-E

the substituent R¹ has a higher priority according to IUPAC (International Union of Pure and Applied Chemistry) than the substituent R². According to IUPAC, the sequence of priority of the substituents is according to the Cahn-Ingold-Prelog rule.

It is generally assumed that the transition metal-catalyzed and specifically the Pd-catalyzed carbonylation proceeds via a pi-allyl complex which makes it possible to obtain respective reaction products comprising the compounds (I) either proceeding from the compounds (II.1) or from the compounds (II.2).

Preferably, the carbonylation is not effected in the presence of an added hydrohalic acid and not in the presence of added alkali metal halide, alkaline earth metal halide or ammonium halide. The expression “ammonium salt” means both salts that derive from NH₄+ and mono-, di-, tri- and tetraorganylammonium salts. Specifically, the carbonylation is not effected in the presence of an added alkyl halide, such as NaCl, NaBr, KCl, KBr, LiCl, LiBr, etc.

Preferably, the halide content of the reaction mixture of the carbonylation is not more than 2 mol %, preferably not more than 1 mol %, based on the content of allyl alcohol of the general formulae (II.1) and (II.2).

In the context of the present invention, the terms “acylated allyl alcohol”, “allyl carboxylate”, “acylation product of allyl alcohol” and “acylation product of an allyl alcohol” are used synonymously.

The expression “aliphatic” in the context of the present invention comprises hydrocarbyl radicals in which the carbon atoms are arranged in straight or branched chains.

The expression “alkyl” and all alkyl moieties in alkoxy, alkylamino and dialkylamino in the context of the present invention comprises saturated, linear or branched hydrocarbon radicals having 1 to 4 (“C₁-C₄-alkyl”), 1 to 6 (“C₁-C₆-alkyl”), 1 to 10 (“C₁-C₁₀-alkyl”), 1 to 20 (“C₁-C₂₀-alkyl”) or 1 to 24 (“C₁-C₂₄-alkyl”) carbon atoms. Examples of linear or branched C₁-C₄-alkyl are methyl, ethyl, n-propyl, 1-methylethyl, n-butyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl. Examples of linear or branched C₁-C₆-alkyl, in addition to the definitions given for C₁-C₄-alkyl, are n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 2,2-dimethylpropyl, 1-ethylpropyl, n-hexyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 3,3-dimethylbutyl, 1-ethylbutyl, 2-ethylbutyl, 1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl, 1-ethyl-1-methylpropyl and 1-ethyl-2-methylpropyl. Examples of linear or branched C₁-C₁₀-alkyl, in addition to the definitions given for C₁-C₆-alkyl, are heptyl, octyl, nonyl, decyl and positional isomers thereof. Examples of C₁-C₂₀-alkyl, in addition to the definitions given for C₁-C₁₀-alkyl, are undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, heneicosyl, docosyl, tricosyl, tetracosyl, pentacosyl, hexacosyl, heptacosyl, octacosyl, nonacosyl, eicosyl and positional isomers thereof.

The expression “alkenyl” in the context of the present invention comprises unsaturated, linear or branched hydrocarbon radicals having 2 to 4 (C₂-C₄-alkenyl), to 6, to 8, to 10, to 16, to 20 or to 24 carbon atoms and one, two, three or more than three double bonds in any position. Examples of linear or branched C₂-C₂₄-alkenyl having one double bond are vinyl, allyl (2-propen-1-yl), 1-methylprop-2-en-1-yl, 2-buten-1-yl, 3-buten-1-yl, n-pentenyl, n-hexenyl, n-heptenyl, n-octenyl, n-nonenyl, n-decenyl, n-undecenyl, n-dodecenyl, n-tridecenyl, n-tetradecenyl, n-pentadecenyl, n-hexadecenyl, n-heptadecenyl, n-octadecenyl, oleyl, n-nona-decenyl, n-eicosenyl, n-heneicosenyl, n-docosenyl, n-tricosenyl, n-tetracosenyl and the constitutional isomers thereof. Examples of linear or branched C₄-C₂₄-alkenyl having two or three double bonds in any position are n-butadienyl, n-pentadienyl, n-hexadienyl, n-heptadienyl, n-octadienyl, n-octatrienyl, n-nonadienyl, n-nonatrienyl, n-decadienyl, n-decatrienyl, n-undecadienyl, n-undecatrienyl, n-dodecadienyl, n-dodecatrienyl, n-tridecadienyl, n-tridecatrienyl, n-tetradecadienyl, n-tetradecatrienyl, n-pentadecadienyl, n-pentadecatrienyl, n-hexadecadienyl, n-hexadecatrienyl, n-heptadecadienyl, n-heptadecatrienyl, n-octadecadienyl, n-octadecatrienyl, n-nonadecadienyl, n-nonadecatrienyl, n-eicosadienyl, n-eicosatrienyl, n-heneicosadienyl, n-heneicosatrienyl, n-docosadienyl, n-docosatrienyl, n-tricosadienyl, n-tricosatrienyl, n-tetracosadienyl, n-tetracosatrienyl, linolenyl and constitutional isomers thereof. Every double bond in C₂-C₂₄-alkenyl may (unless stated otherwise) in each case independently be in the E configuration or in the Z configuration.

The expression “cycloalkyl” in the context of the present invention comprises monocyclic saturated hydrocarbon radicals having 3 to 8 (“C₃-C₈-cycloalkyl”), preferably 5 to 7 carbon ring members (“C₅-C₇-cycloalkyl”). Examples of C₃-C₈-cycloalkyl are cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl.

The expression “heterocyclyl” (also referred to as heterocycloalkyl) in the context of the present invention encompasses monocyclic saturated cycloaliphatic groups having generally 5 to 8 ring atoms, preferably 5 or 6 ring atoms, in which 1 or 2 of the ring carbon atoms are replaced by heteroatoms or heteroatom-containing groups selected from oxygen, nitrogen, NH and N(C₁-C₄-alkyl). Examples of such heterocycloaliphatic groups are pyrrolidinyl, piperidinyl, tetrahydrofuranyl and tetrahydropyranyl.

The expression “aryl” in the context of the present invention comprises a mono-, di- or tricyclic aromatic ring system comprising 6 to 20 carbon ring members. Examples of unsubstituted C₆-C₁₀-aryl are phenyl and naphthyl. Examples of C₆-C₁₄-aryl are phenyl, naphthyl, anthracenyl and phenanthrenyl. Substituted aryl groups generally bear 1, 2, 3, 4 or 5 identical or different substituents, preferably 1, 2 or 3 substituents. Suitable substituents are especially selected from alkyl, cycloalkyl, aryl, alkoxy, dialkylamino. Examples of aryl that bears 1, 2 or 3 substituents selected from C₁-C₆-alkyl are tolyl, xylyl and mesityl.

The expression “hetaryl” in the context of the present invention comprises a five- to six-membered aromatic heteromonocycle comprising one, two, three or four heteroatoms from the group of oxygen, nitrogen and sulfur, and 9- or 10-membered aromatic heterobicycles, e.g. carbon-bonded 5-membered heteroaryl comprising one to three nitrogen atoms or one or two nitrogen atoms and one sulfur or oxygen atom as ring members, such as furyl, thienyl, pyrrolyl, isoxazolyl, isothiazolyl, pyrazolyl, oxazolyl, thiazolyl, imidazolyl, 4-imidazolyl, 1,2,4-oxadiazolyl, 1,2,4-thiadiazolyl, 1,2,4-triazolyl, 1,3,4-oxadiazolyl; nitrogen-bonded 5-membered heteroaryl comprising one to three nitrogen atoms as ring members, such as pyrrol-1-yl, pyrazol-1-yl, imidazol-1-yl, 1,2,3-triazol-1-yl and 1,2,4-triazol-1-yl; 6-membered heteroaryl comprising one to three nitrogen atoms as ring members, such as pyridinyl, pyridazinyl, pyrimidinyl, pyrazinyl, 1,3,5-triazinyl and 1,2,4-triazinyl.

Halogen is fluorine, chlorine, bromine or iodine. Halide is fluoride, chloride, bromide or iodide.

Alkali metals correspond to the group 1 elements of the Periodic Table of the Elements according to IUPAC, for example lithium, sodium, potassium, rubidium or cesium, preferably lithium, sodium or potassium, especially sodium or potassium.

Alkaline earth metals correspond to the group 2 elements of the Periodic Table of the Elements according to IUPAC, for example beryllium, magnesium, calcium, strontium or barium, preferably magnesium or calcium.

Group 8 of the Periodic Table of the Elements according to IUPAC comprises, inter alia, iron, ruthenium and osmium. Group 9 of the Periodic Table of the Elements according to IUPAC comprises, inter alia, cobalt, rhodium, iridium. Group 10 of the Periodic Table of the Elements according to IUPAC comprises, inter alia, nickel, palladium and platinum.

The expression “ammonium salts” in the context of the present invention comprises both salts that derive from NH₄+ and mono-, di-, tri- and tetraorganylammonium salts. The radicals bonded to the ammonium nitrogen are generally each independently selected from hydrogen and aliphatic, alicyclic and aromatic hydrocarbon groups. Preferably, the radicals bonded to the ammonium nitrogen are each independently selected from hydrogen and aliphatic radicals, especially selected from hydrogen and C₁-C₂₀-alkyl.

The expression “acyl” in the context of the present invention comprises alkanoyl or aroyl groups having generally 1 to 11 and preferably 2 to 8 carbon atoms, for example the formyl, acetyl, propionyl, butyryl, pentanoyl, benzoyl or naphthoyl group.

Acetylation in the context of the present invention is the exchange of hydrogen for an acetyl group (—C(═O)—CH₃).

Unless stated more specifically hereinafter, the general formulae (I), (II.2), (III.2) and (IV.2) refer to E/Z mixtures of any composition and the pure configurational isomers. In addition, the general formulae (I), (II.2), (III.2) and (IV.2) refer to all stereoisomers in pure form and to racemic and optically active mixtures of the compounds of the formulae (II.2), (III.2) and (IV.2).

“Stereoisomers” are compounds of the same constitution but different atomic arrangement in three-dimensional space.

“Enantiomers” are stereoisomers which behave with respect to one another like an image and mirror image.

The term “terpene-like hydrocarbyl radicals” in the context of the present invention comprises hydrocarbyl radicals that derive in a formal sense from one, two, three or more than three isoprene units. The terpene-like hydrocarbyl radicals may still have double bonds or may be fully saturated. The double bonds can assume any desired positions, excluding cumulated double bonds.

The term “farnesol (3,7,11-trimethyl-2,6,10-dodecatrien-1-ol)” in the context of the present invention comprises the (2E,6E), (2Z,6Z), (2Z,6E) and (2E,6Z) isomers and mixtures of two, three or all the isomers of farnesol mentioned. Farnesol is commercially available.

Nerolidol has one chiral center and may be in the form of an E/Z mixture, meaning that there are four stereoisomers. The term “nerolidol (3,7,11-trimethyl-1,6,10-dodecatrien-3-ol)” in the context of the present invention comprises the (3S), (6Z) isomer, (3R), (6Z) isomer, (3S), (6E) isomer, (3R), (6E) isomer and any desired mixtures thereof. Nerolidol is commercially available. Nerolidyl acetate (3,7,11-trimethyl-1,6,10-octatrienyl acetate) is the acetylation product of nerolidol. It is likewise commercially available.

Another name for homofarnesylic acid is 4,8,12-trimethyltrideca-3,7,11-trienoic acid.

A first embodiment of the present invention (variant 1) relates to the carbonylation of an allylic alcohol (allyl alcohol) selected from compounds of the formulae (II.1) and (II.2) to give the corresponding C1-extended unsaturated carboxylic acids of the formula (I).

The starting compounds of the formula (II.1) are commercially available or can be prepared, for example, from the corresponding carbonyl compounds R¹—CO—R² and vinylmagnesium halides. The compounds of the formula (II.1) can also be prepared from the corresponding carbonyl compound and acetylides such as sodium acetylide and subsequent partial hydrogenation of the ethynyl group to give the vinyl group.

Allyl alcohols of the formula (II.1) and (II.2) that are preferred in the context of the process of the invention are those in which the R¹ and R² radicals are the same or different and are hydrogen, linear or branched C₁-C₁₆-alkyl, linear or branched C₂-C₁₆-alkenyl having one or two nonconjugated double bonds, or R¹ and R² together with the carbon atom to which they are bonded are unsubstituted C₅-C₇-cycloalkyl or C₅-C₇-cycloalkyl bearing 1, 2 or 3 linear or branched C₁-C₆-alkyl radicals.

Especially preferred are compounds of the formulae (II.1) and (II.2) having terpene-like hydrocarbyl radicals. R¹ is preferably linear or branched C₆-C₁₆-alkyl or linear or branched C₆-C₁₆-alkenyl having one or two nonconjugated double bonds. R² is preferably hydrogen or C₁-C₄-alkyl, especially C₁-C₂-alkyl. Allyl alcohols of the formula (II.1) that are particularly preferred in accordance with the invention are 3-methyl-1-penten-3-ol, 1-hepten-3-ol, 1-vinylcyclohexanol, linalool and nerolidol, especially linalool and nerolidol, specifically 6E-nerolidol. Allyl alcohols of the formula (II.2) which are particularly preferred in accordance with the invention are geraniol and farnesol.

If the compounds of the formulae (II.1) and (II.2) have one or more centers of asymmetry, it is also possible to use enantiomer mixtures or diastereomer mixtures. The process of the invention can be conducted with a mixture of the compounds of the formulae (II.1) and (II.2).

According to the invention, the process is executed according to variant 1 in which an allyl alcohol selected from compounds of the general formulae (II.1) and (II.2) is used for the reaction, in the presence of a compound A). Useful compounds A) preferably include the anhydrides of linear or branched monobasic C₁-C₁₂-alkanecarboxylic acids. Examples of such anhydrides are acetic anhydride, propionic anhydride, isopropionic anhydride, butyric anhydride, n-valeric anhydride, the mixed anhydride of formic acid and acetic acid, and the like. Especially preferred are the symmetric anhydrides of the alkanemonocarboxylic acids having up to 5 carbon atoms. Likewise suitable are the anhydrides of linear or branched monobasic C₃-C₁₂-alkenecarboxylic acids. Examples of these are (meth)acrylic anhydride, crotonic anhydride and isocrotonic anhydride. Likewise suitable are the anhydrides of linear or branched dibasic C₄-C₂₀-alkanecarboxylic acids, for example the anhydride of succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassylic acid, tetradecanedioic acid, pentadecanedioic acid, hexadecanedioic acid, heptadecanedioic acid, octadecanedioic acid. Likewise suitable are the anhydrides of linear or branched dibasic C₄-C₂₀-alkenecarboxylic acids, for example maleic anhydride or itaconic anhydride. Likewise suitable are the anhydrides of cycloaliphatic C₇-C₂₀-dicarboxylic acids such as cyclopentanedicarboxylic anhydride or cyclohexanecarboxylic anhydride. Likewise suitable are the anhydrides of aromatic C₈-C₂₀-dicarboxylic acids, such as phthalic anhydride, 1,8-naphthalenecarboxylic anhydride or 2,3-naphthalenecarboxylic anhydride. Particular preference is given to using acetic anhydride, propionic anhydride, isopropionic anhydride, butyric anhydride, succinic anhydride, maleic anhydride or phthalic anhydride, especially acetic anhydride.

Suitable compounds A) are likewise the esters of the formulae (III.1) and (III.2). In the process of the invention, it does not matter whether the double bond is arranged in a terminal position (compound of the formula (III.1)) or whether the double bond is arranged in an internal position (compound of the formula (III.2)). Therefore, it is also possible to use a mixture of compounds of the formulae (III.1) and (III.2). In general, however, no mixture of the compounds of the formulae (III.1) and (III.2) is used.

Preference is given to compounds of the formulae (III.1) and (III.2) in which the R³ and R⁴ radicals are the same or different and are hydrogen, linear or branched C₁-C₁₆-alkyl, linear or branched C₂-C₁₆-alkenyl having one or two nonconjugated double bonds, or R³ and R⁴ together with the carbon atom to which they are bonded are unsubstituted C₅-C₇-cycloalkyl or C₅-C₇-cycloalkyl bearing 1, 2 or 3 linear or branched C₁-C₆-alkyl radicals. Alternatively, in the compounds of the formulae (III.1) and (III.2), R³ and R⁴ together with the carbon atom to which they are bonded are preferably unsubstituted C₅-C₇-cycloalkyl. In the compounds of the formulae (III.1) and (III.2), R⁵ is preferably hydrogen or C₁-C₄-alkyl. Specifically, R⁵ is C₁-C₂-alkyl. Particular preference is given to allyl acetate.

Likewise preferred as compound A) is an ester of the formula (III.1) or (III.2) which derives from the alcohol of the formula (II.1) or (II.2) used as reactant for the carbonylation. Esters of the formula (III.1) that are particularly preferred in accordance with the invention are esters of a linear or branched monobasic C₁-C₃-alkanecarboxylic acid and an alcohol selected from 3-methyl-1-penten-3-ol, 1-hepten-3-ol, 1-vinylcyclohexanol, linalool and nerolidol. Especially preferred are linaloyl acetate and nerolidyl acetate, specifically 6E-nerolidyl acetate. A compound of the formula (III.2) which is particularly preferred in accordance with the invention is farnesyl acetate.

If the compounds of the formulae (III.1) and (III.2) have one or more centers of asymmetry, it is also possible to use enantiomer mixtures or diastereomer mixtures.

In variant 1, in which an allyl alcohol selected from compounds of the general formulae (II.1) and (II.2) is used for the reaction, the carbonylation is effected in accordance with the invention in the presence of a substoichiometric amount, based on the allyl alcohol used, of a compound A), i.e. the molar amount of compound A) is less than the molar amount of allyl alcohol. The molar ratio of compound A) to the allyl alcohol selected from compounds of the formulae (II.1) and (II.2) is typically in the range from 0.001:1 to about 0.95:1. Preferably, the total amount of the compound A) is not more than 50 mol %, preferably not more than 40 mol %, preferably not more than 30 mol %, based on the total molar amount of the compounds (II.1) and (II.2). Molar ratios in the range from 0.1:1 to 0.35:1 and specifically from 0.15:1 to 0.30:1 are particularly preferred.

In the processes of the invention for preparation of the carboxylic acid of the formula (I), the effect of the added anhydride is equivalent to the effect of the acylated allyl alcohol of the formulae (III.1) and (III.2) added.

In addition, it may be appropriate to conduct the carbonylation according to variant 1 in the presence of a nucleophilic reagent. Examples of nucleophilic reagents are 4-(C₁-C₄-alkyl)pyridines, 4-(1-pyrrolidinyl)pyridine and 4-(di(C₁-C₄-alkyl)amino)pyridine. Suitable 4-(C₁-C₄-alkyl)pyridines are 4-methylpyridine and 4-ethylpyridine. Suitable 4-(di(C₁-C₄-alkyl)amino)-pyridines are 4-(dimethylamino)pyridine and 4-(diethylamino)pyridine, especially 4-dimethylaminopyridine. Typically, the nucleophilic reagent selected from 4-(C₁-C₄-alkyl)pyridine, 4-(1-pyrrolidinyl)pyridine and 4-(di(C₁-C₄-alkyl)amino)pyridine is used in an amount of 0.01 to 5 mol %, preferably of 0.05 to 2 mol %, especially of 0.1 to 1 mol %, based on the total molar amount of the compounds (II.1) and (II.2).

The remarks which follow relating to the preparation of a composition comprising at least one unsaturated carboxylic acid of the general formula (I) relate to all variants of the process of the invention (variant 1, variant 2 and variant 3), unless explicitly stated otherwise.

In all variants, the upper limit for the amount of carbon monoxide is determined by economic reasons, although the use of an excess amount does not adversely affect the reaction. Advantageously, carbon monoxide is used in excess. Carbon monoxide is usually used in an amount of at least 1.1 mol per total molar amount of the compounds (II.1) and (II.2) or per total molar amount of the compounds (IV.1) and (IV.2).

The carbonylation (by all variants) is effected in accordance with the invention in the presence of a transition metal catalyst comprising at least one metal of group 8, 9 or 10 of the Periodic Table of the Elements. Transition metals used are preferably palladium, ruthenium, rhodium, iridium and iron, more preferably palladium.

Typically, the transition metal catalyst is used in an amount of not more than 0.5 mol %, in particular 0.001 to 0.3 mol %, based on the total amount of the compounds (II.1) and (II.2) or based on the total amount of the compounds (IV.1) and (IV.2).

According to the invention, at least one organic phosphorus compound is additionally used as ligand. Suitable organic phosphorus compounds are monodentate and bidentate phosphorus ligands. The nature of the organic phosphorus compound is unimportant in principle, and so it is generally advisable to use inexpensive tertiary monodentate phosphines of the formula (V)

in which

-   R⁷, R⁸ and R⁹ are independently selected from unsubstituted and     substituted alkyl, unsubstituted and substituted cycloalkyl,     unsubstituted and substituted heterocyclyl, unsubstituted and     substituted aryl and unsubstituted and substituted hetaryl.

Preferably, R⁷, R⁸ and R⁹ are independently

-   -   C₁-C₁₆-alkyl which is unsubstituted or substituted by phenyl;     -   C₅-C₈-cycloalkyl which is unsubstituted or substituted by 1, 2         or 3 C₁-C₆-alkyl radicals;     -   C₆-C₁₀-aryl which is unsubstituted or substituted by 1, 2 or 3         C₁-C₆-alkyl radicals, C₁-C₆-alkoxy radicals,         di(C₁-C₄-dialkyl)amino, SO₃H or SO₃M where M is Li, Na, K, NH₄;     -   C₆-C₁₀-aryl substituted by 1, 2 or 3 radicals selected from         fluorine, chlorine and C₁-C₁₀-fluoroalkyl;     -   5- or 6-membered saturated heterocyclyl comprising, as well as         carbon atoms, a nitrogen atom or an oxygen atom as ring member;     -   C₅-C₈-Cycloalkyl; or     -   5- or 6-membered hetaryl comprising, as well as carbon atoms, a         heteroatom selected from nitrogen and oxygen.

Examples of preferred phosphines of the formula (V) are trialkylphosphines, triarylphosphines, dialkylarylphosphines, alkyldiarylphoshines, cycloalkyldiaryiphosphines, dicycloalkylarylphosphines, and tricycloalkylphosphines. Examples of preferred phosphines of the formula (V) are likewise triheterocyclylphosphines and trihetarylphosphines. Examples of preferred trialkylphosphines are triethylphosphine, tri-n-butylphosphine, tri-tert-butylphosphine, tribenzylphosphine, etc. Examples of preferred tricycloalkylphosphines are tri(cyclopentyl)phosphine, tri(cyclo-hexyl)phosphine, etc. Examples of preferred triarylphosphines are triphenylphosphine, tri(p-tolyl)phosphine, tri(m-tolyl)phosphine, tri(o-tolyl)phosphine, tri(p-methoxyphenyl)phosphine, tri(p-dimethylaminophenyl)phosphine, tri(sodium meta-sulfonatophenyl)phosphine, diphenyl(2-sulfonatophenyl)phosphine, tri(1-naphthyl)phosphine and diphenyl-2-pyridylphosphine. Examples of preferred dialkylarylphosphine are dimethylphenylphosphine and di-tert-butylphenylphosphine. Examples of preferred alkyldiarylphosphines are ethyldiphenylphosphine and isopropyldiphenylphosphine. One example of preferred cycloalkyldiaryiphosphine is cyclohexyldiphenylphosphine. One example of preferred dicycloalkylarylphosphine is dicyclohexylphenylphosphine. Further examples of preferred triarylphosphines are tri(o-methoxyphenyl)phosphine, tri(m-methoxyphenyl)phosphine, tri(p-fluorophenyl)phosphine, trim-fluorophenyl)phosphine, tri(o-fluorophenyl)phosphine, tri(p-chlorophenyl)phosphine, tri(m-chlorophenyl)phosphine, tri(pentafluorophenyl)phosphine, tris(p-trifluoromethylphenyl)phosphine, tri[3,5-bis(trifluoromethyl)phenyl]phosphine, diphenyl(o-methoxyphenyl)phosphine, diphenyl(o-methylphenyl)phosphine, tris(3,5-dimethylphenyl)phosphine and tri-2-naphthylphosphine. One example of preferred trihetarylphosphine is tri(o-furyl)phosphine. A further example of preferred trialkylphosphine is triisobutylphosphine. One example of preferred trihetercyclylphosphine is tris(1-pyrrolidinyl)phosphine. Especially preferred are triphenylphosphine, di-tert-butylphenyiphosphine, cyclohexyldiphenylphosphine, dicyclohexylphenylphosphine, tri(p-tolyl)phosphine and tri(cyclohexyl)phosphine.

Suitable bidentate phosphine ligands are 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (BINAP), 2-bis(diphenylphosphino)ethane (DPPE), 1,3-bis(diphenylphosphino)propane (DPPP), 1,4-bis(diphenylphosphino)butane (DPPB), 1,1′-bis(diphenylphosphino)ferrocene (DPPF), 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (Xantphos), 1,2-bis(di-tert-butylphosphinomethyl)benzene, 1,2-bis(di-tert-pentylphosphinomethyl)benzene and 1,2-bis(di-tert-butylphosphinomethyl)naphthalene.

In addition, it may be appropriate to conduct the reaction in the presence of phosphine of the formula (V) in free form, i.e. not bound within the complex, and/or bidentate phosphines.

The molar ratio of organic phosphorus compound to transition metal is typically 1:1 to 10:1, preferably 2:1 to 5:1, Specifically, the molar ratio of organic phosphorus compound of the formula (V) to transition metal is typically 1:1 to 10:1, preferably 2:1 to 5:1.

It is advantageous to conduct the carbonylation with exclusion of or with a reduced content of atmospheric oxygen.

In addition to the organic phosphorus compounds described as ligand above, the carbonylation catalysts used in accordance with the invention may also include at least one further ligand preferably selected from halides, amines, acetate, carboxylates, acetylacetonate, aryl- or alkylsulfonates, hydride, CO, olefins, dienes, cycloolefins, nitriles, N-containing heterocycles, aromatics and heteroaromatics, ethers and monodentate phosphinite, phosphonite, phosphoramidite and phosphite ligands. Particularly suitable further ligands are carbonyl, acetate, acetylacetonate and cycloolefins such as cyclooctadiene or norbornadiene. Halides are likewise suitable, specifically chlorides and bromides.

Suitable transition metal sources are quite generally transition metals, transition metal compounds and transition metal complexes, from which the carbonylation catalyst is formed in situ under the carbonylation conditions in the reaction zone.

Suitable compounds of the transition metals mentioned are especially those that are soluble in the reaction medium chosen, for example salts or complexes with suitable ligands, for example carbonyl, acetylacetonate, hydroxyl, cyclooctadiene, norbornadiene, cyclooctene, methoxy, acetyl or other aliphatic or aromatic carboxylates. Transition metal compounds that are preferred in the context of the process of the invention are Ru(II), Ru(III), Ru(IV), Ru(0), Rh(I), Rh(III), Rh(0), Ir(I), Ir(III), Ir(IV), Ir(0) compounds, Pd(II), Pd(IV), Pd(0), Pt(II), Pt(IV), Pt(0) compounds and Fe(II) and Fe(III) compounds.

Suitable ruthenium salts are, for example, ruthenium(III) chloride, ruthenium(IV) oxide, ruthenium(VI) oxide or ruthenium(VIII) oxide, alkali metal salts of the ruthenium-oxygen acids, such as K₂RuO₄ or KRuO₄, or complexes of ruthenium. These include the metal carbonyls, such as trisruthenium dodecacarbonyl or hexaruthenium octadecacarbonyl, or mixed forms in which CO has been partly replaced by ligands of the formula PR⁷R⁸R⁹, such as Ru(CO)₃(P(C₆H₅)₃)₂ or tris(acetylacetonato)ruthenium(III).

Examples of transition metal sources for suitable palladium compounds or complexes include palladium(II) acetate, palladium(II) chloride, palladium(II) bromide, palladium(II) nitrate, palladium(II) acetylacetonate, palladium(0) dibenzylideneacetone complex, tetrakis(triphenylphosphine)palladium(0), bis(tri-o-tolylphosphine)palladium(0), palladium(II) propionate, bis(triphenylphosphine)palladium(II) dichloride, palladium(II) nitrate, bis(acetonitrile)palladium(II) dichloride, bis(benzonitrile)palladium(II) dichloride.

Examples of rhodium compounds or complexes suitable as transition metal source include rhodium(II) and rhodium(III) salts, such as rhodium(II) or rhodium(III) carboxylate, rhodium(II) and rhodium(III) acetate, etc. Additionally suitable are rhodium complexes, such as rhodium biscarbonyl acetylacetonate, acetylacetonatobisethylenerhodium(I), acetyl-acetonatocyclooctadienylrhodium(I), acetylacetonatonorbornadienylrhodium(I), acetyl-acetonatocarbonyltriphenylphosphinerhodium(I), Rh₄(CO)₁₂, Rh₆(CO)₁₈ etc.

Iron compounds suitable as transition metal source are Fe₂(CO)₁₀, Fe₂(CO)₉, tris(acetylacetonato)iron(III).

The catalyst used may be homogeneously dissolved in the liquid reaction medium or, in the case of a polyphasic reaction, may be dissolved in the liquid phase of the reaction medium as what is called a homogeneous catalyst, or may be in supported or unsupported form as what is called a heterogeneous catalyst.

If the conversion is effected in the absence of further coreactants, the acid of the formula (I) is obtained. The acid of the formula (I) obtained can be removed from the reaction mixture by methods known per se to those skilled in the art, for example by distillation, and the remaining catalyst can be utilized in further reactions. The acid of the formula (I) can also be obtained by extracting from the reaction mixture.

The carbonylation can (in all variants) be conducted in the presence or absence of a base. The base is different than the nucleophilic reagent. Suitable bases are inorganic and organic bases. Examples of preferred inorganic bases are alkali metal carbonates and alkaline earth metal carbonates. Preferred alkali metals are sodium and potassium, particular preference being given to sodium. Preferred alkaline earth metals are magnesium and calcium. Suitable bases are likewise organic bases other than the nucleophilic reagent which is selected from 4-(C₁-C₄-alkyl)pyridine, 4-(1-pyrrolidinyl)pyridine and 4-(di-(C₁-C₄-alkyl)amino)pyridine such as 4-(dimethylamino)pyridine. The presence of the base, for example an additional amine, promotes the formation of the salt of the carboxylic acid of the general formula (I), such that the conversion rate is distinctly improved. In addition, acids which form from the anhydrides under the reaction conditions are neutralized or buffered by the base. It is possible in turn to generate the free acid from the salts of the carboxylic acid of the formula (I) by thermal means, for example by distillation of the reaction output, or by acidifying. Preference is given to effecting the carbonylation in the presence of an amine other than the nucleophilic reagent such as 4-(dimethylamino)pyridine. More particularly, a tertiary amine or a basic N-heteroaromatic is used.

Examples of the tertiary amine comprise a trialkylamine, specifically a tri(C₁-C₁₅-alkyl)amine such as trimethylamine, triethylamine, tripropylamine, tributylamine, trihexyl-amine, trioctylamine, tridecylamine, N,N-dimethylethylamine, dimethylpropylamine or 1,4-diaza-bicyclo[2.2.2]octane (DABCO); an aromatic amine such as dimethylaniline or tribenzylamine; a cyclic amine such as N-methylpyrrolidine, N-methylpiperidine, N-methylmorpholine, N,N′-dimethylpiperazine. Among these, preference is given to a trialkylamine, such as triethylamine. Likewise suitable are N-heteroaromatics such as pyridine, N-methylimidazole or quinoline. The base other than the nucleophilic reagent selected from 4-(C₁-C₄-alkyl)pyridine, 4-(1-pyrrolidinyl)pyridine and 4-(di-(C₁-C₄-alkyl)amino)pyridine such as 4-(dimethylamino)-pyridine, is typically used in an amount of 0.8 mol to 1.2 mol per mole of the compound (I).

Especially in the case of carbonylation in the presence of an amine, acidification of the reaction mixture and extraction is a suitable method of obtaining the free acid. Alternatively, the free acid can be separated from the reaction mixture by distillation, since the salt of the unsaturated acid of the formula (I) breaks down under the action of heat to give the free unsaturated acid of the formula (I) and the amine,

The carbonylation (in all variants) can be effected in the presence or absence of an added inert solvent. Inert solvents are understood to mean solvents that do not react chemically under the reaction conditions with the compounds used, i.e. the reactants, the products and the catalysts. Suitable inert solvents are aprotic organic solvents, for example aromatic hydrocarbons such as toluene or xylenes, alicyclic hydrocarbons such as cyclohexane, and cyclic ethers such as tetrahydrofuran or dioxane. For practical reasons, the carbonylation is preferably conducted in the absence of an inert solvent. If the reactant used, however, is sparingly soluble under the reaction conditions, the use of a solvent is advisable.

The carbonylation can be conducted continuously, semicontinuously or batchwise.

The pressure (in all variants) can be chosen within a wide range such as from atmospheric pressure to not more than 90 bar, preferably to not more than 30 bar, more preferably to not more than 25 bar, more preferably not more than 20 bar and especially not more than 15 bar. Suitable pressure ranges are, for example, 1.1 to 90 bar, 1.1 to 30 bar, 2 to 20 bar, 5 to 15 bar.

The reaction temperature (in all variants) can be chosen within a wide range from room temperature (25° C.) to 100° C., but it is preferably not more than 80° C., especially not more than 75° C.

In a specific embodiment of the process of the invention, the carbonylation is effected at a temperature of not more than 90° C. and at a pressure of not more than 20 bar.

Suitable pressure-resistant reactors are likewise known to those skilled in the art and are described, for example, in Ullmanns Enzyklopadie der technischen Chemie [Ullmann's Encyclopedia of Industrial Chemistry], vol. 1, 3rd edition, 1951, p. 769 ff. In general, an autoclave which may be provided if desired with a stirrer apparatus and an inner lining is used for the process of the invention.

The catalysts used in accordance with the invention can be separated from the output of the carbonylation reaction by customary methods known to those skilled in the art and can be reused for a carbonylation.

The reaction mixture can be subjected to a workup by customary methods known to those skilled in the art. For this purpose, the reaction mixture obtained in the carbonylation can be subjected to at least one workup step for removal of at least one of the following components:

-   -   carbonylation catalyst,     -   unconverted compounds of the formulae (II.1) and (II.2) or         (IV.1) and (IV.2),     -   reaction products other than the compounds of the formula (I),     -   solvents.

A further embodiment of the present invention (variant 2) relates, as explained above, to the carbonylation of an acylated allyl alcohol selected from compounds of the formulae (IV.1) and (IV.2) to give the corresponding C1-extended unsaturated carboxylic acids of the formula (I) or a salt thereof, comprising the reaction of compounds selected from compounds of the formulae (IV.1) and (IV.2) with carbon monoxide in the presence of a transition metal catalyst comprising at least one metal of group 8, 9 or 10 of the Periodic Table of the Elements, wherein the reaction is additionally effected in the presence of at least one organic phosphorus compound as ligand and in the presence of water and wherein the reaction is effected at a temperature of not more than 100° C.

Compounds of the formulae (IV.1) and (IV.2) that are preferred in the context of the process of the invention are those in which the R¹ and R² radicals are the same or different and are hydrogen, linear or branched C₁-C₁₆-alkyl, linear or branched C₂-C₁₆-alkenyl having one or two nonconjugated double bonds, or R¹ and R² together with the carbon atom to which they are bonded are unsubstituted C₅-C₇-cycloalkyl or C₅-C₇-cycloalkyl bearing 1, 2 or 3 linear or branched C₁-C₆-alkyl radicals.

Especially preferred are compounds of the formulae (IV.1) and (IV.2) with terpene-like hydrocarbyl radicals. R¹ is preferably linear or branched C₆-C₁₆-alkyl or linear or branched C₆-C₁₆-alkenyl having one or two nonconjugated double bonds. R² is preferably hydrogen or C₁-C₄-alkyl, especially C₁-C₂-alkyl. R⁶ is preferably C₁-C₂-alkyl. Particular preference is given in accordance with the invention to esters of a linear or branched monobasic C₁-C₃-alkanecarboxylic acid and of an allylic alcohol selected from 3-methy-1-penten-3-ol, 1-hepten-3-ol, 1-vinylcyclohexanol, linalool and nerolidol. Particular preference is given in accordance with the invention to linaloyl acetate and nerolidyl acetate, specifically 6E-nerolidyl acetate. A compound of the formula (IV.2) which is particularly preferred in accordance with the invention is farnesyl acetate.

If the compounds of the formulae (IV.1) and (IV.2) have one or more centers of asymmetry, it is also possible to use enantiomer mixtures or diastereomer mixtures. The process of the invention can be conducted with a mixture of the compounds of the formulae (IV.1) and (IV.2). However, preference is given to using a compound either of the formula (IV.1) or of the formula (IV.2).

Compounds of the formula (IV.1) are obtainable, for example, by esterifying carboxylic acids of the formula R⁶—C(O)OH with the allyl alcohol of the formula (II.1), and compounds of the formula (IV.2), for example, by esterifying carboxylic acids of the formula R⁶—C(O)OH with the allyl alcohol of the formula (II.2).

According to the invention, the carbonylation is effected in the presence of water. The molar ratio of water to the total molar amount of compounds of the formulae (IV.1) and (IV.2) is typically in the range from 1:1 to 10:1, but preferably in the range from 1.1:1 to 3:1.

With regard to suitable transition metal catalysts, suitable organic phosphorus compounds as ligand, reaction temperature, reaction pressure, reaction time, use of solvent, use of a nucleophilic reagent, use of bases other than the nucleophilic reagent, specifically the use of amines other than 4-(dimethylamino)pyridine and reaction apparatuses, reference is made to the above statements.

A further embodiment of the present invention (variant 3) relates, as stated above, to the carbonylation of compounds of the general formulae (II.1) and (II.2) to give the corresponding C-1-extended unsaturated carboxylic acids of the formula (I) or a salt thereof, comprising the reaction of compounds selected from compounds of the formulae (II.1) and (II.2) with carbon monoxide in the presence of a transition metal catalyst comprising at least one metal of groups 8, 9 and 10 of the Periodic Table of the Elements, wherein the reaction is additionally effected in the presence of at least one organic phosphorus compound as ligand and in the presence of a substoichiometric amount, based on the allyl alcohol, of a compound B), and wherein the reaction is effected at a temperature of not more than 100° C. In the compounds B, R¹⁰ and R¹¹ preferably have the same meaning. Useful compounds B) preferably include methanesulfonic anhydride, trifluoromethanesulfonic anhydride, phenylsulfonic anhydride, p-toluenesulfonic anhydride, 4-bromophenylsulfonic anhydride and 4-nitrophenylsulfonic anhydride.

In variant 3, in which an allyl alcohol selected from compounds of the general formulae (II.1) and (II.2) is used for reaction, the carbonylation, according to the invention, is effected in the presence of a substoichiometric amount, based on the allyl alcohol used, of a compound B), meaning that the molar amount of compound B) is less than the molar amount of allyl alcohol. The molar ratio of compound B) to the allyl alcohol selected from compounds of the formulae (II.1) and (II.2) is typically in the range from 0.001:1 to about 0.95:1. Preferably, the total amount of the compound B) is not more than 50 mol %, preferably not more than 40 mol %, based on the total molar amount of the compounds (II.1) and (II.2). Molar ratios in the range from 0.1:1 to 0.35:1 and especially from 0.15:1 to 0.30:1 are particularly preferred.

In the processes of the invention for preparing the carboxylic acid of the formula (I) by variant 3, the effect of the added sulfonic anhydride is equivalent to the effect of the added compound A) in variant 1.

With regard to suitable transition metal catalysts, suitable organic phosphorus compounds as ligand, reaction temperature, reaction pressure, reaction time, use of solvents, use of nucleophilic agents, use of bases other than nucleophilic reagent, and reaction apparatuses, reference is made to the above statements.

The carbonylation by variant 3 is preferably effected at a temperature of not more than 100° C. and at a pressure of not more than 30 bar.

In the variants 1, 2 and 3 of the process of the invention, it is possible to obtain homofarnesylic acid proceeding from commercial substances, such as farnesol or nerolidol, in high yield under mild reaction conditions.

More particularly, the process of the invention is suitable for preparing E/Z-4,8-dimethyl-3,7-nonadienoic acid from linalool under mild reaction conditions.

More particularly, the process of the invention is likewise suitable for preparation of (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid or a salt thereof and (3Z,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid or a salt thereof in a weight ratio of 80:20 to 50:50, preferably of 70:30 to 55:45, proceeding from E-nerolidol. The proportion of (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid in the isomer mixtures obtained is generally higher than the proportion of (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid. The composition obtained can be subjected to an at least partial enrichment of one isomer.

In the processes according to variants 1, 2 and 3, in general, E/Z isomer mixtures of the formula (I) or salts thereof are obtained when R¹ and R² in formula (I) have different meanings. The E/Z isomer mixtures of the formula (I) comprise a 3-(E) acid of the formula (I-E) and a 3-(Z) acid of the formula (I-Z)

in which R¹ and R² have different definitions and R¹ has a higher priority according to IUPAC.

Frequently, just one of the two isomers is the product of value. Preference is given to subjecting the E/Z isomer mixture of the formula (I) which is obtained by the process of the invention to an at least partial enrichment of one isomer. A possible isomer separation of such a mixture for partial enrichment of one isomer can be effected by chromatography or distillation or as described in EP 17157974.1.

The product of value is frequently the 3-(E) acid of the formula (I-E), and not the 3-(Z) acid of the formula (I-Z) which is likewise obtained in significant amounts.

It would therefore be economically advisable first to separate at least a portion of the 3-(E) acid of the formula (I-E) from the composition obtained in accordance with the invention comprising the E/Z isomer mixture of the formula I, and to convert the unwanted 3-(Z) acid of the formula (I-Z) at least partly to the product of value, i.e. to the 3-(E) acid of the formula (I-E).

Therefore, in a preferred embodiment of the present invention, the process of the invention for preparing an E/Z isomer mixture of the formula (I) comprises the following additional steps:

-   -   (1) the composition comprising the E/Z isomer mixture of the         formula (I), in the presence of an alcohol and of a lipase         enzyme, is subjected to an enzyme-catalyzed esterification,         wherein the 3-(E) acid of the formula (I-E) is converted at         least partly to a 3-(E) ester, so as to obtain a composition         comprising the 3-(E) ester, unconverted 3-(E) acid of the         formula (I-E) and unconverted 3-(Z) acid of the formula (I-Z);     -   (2) the composition obtained in (1) is separated to obtain a         composition depleted of 3-(E) acid of the formula (I-E) and         enriched in 3-(Z) acid of the formula (I-Z), and to obtain a         composition comprising the 3-(E) ester,     -   (3) the composition obtained in (2) which is depleted of 3-(E)         acid of the formula (I-E) and enriched in 3-(Z) acid of the         formula (I-Z) is subjected to an isomerization to increase the         content of 3-(E) acid of the formula (I-E), and     -   (4) optionally, the 3-(E) ester obtained in (2) is cleaved to         obtain the 3-(E) acid of the formula (I-E).

Processes for enzymatically catalyzed esterifications of a mixture of 3-(E)-unsaturated carboxylic acid and 3-(Z)-unsaturated carboxylic acid with an alcohol are known, for example, from EP 17157974.1.

Many lipases are capable of catalyzing esterifications with high substrate selectivity. Preferably, the lipase is Candida antarctica lipase (CALK) or a form immobilized on a polymeric carrier, such as Novozym 435®. The enzyme-catalyzed esterification is preferably effected in the presence of an aliphatic alcohol. Suitable aliphatic alcohols are C₁-C₂₀-alkanols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, n-pentanol, n-hexanol, n-heptanol and n-octanol. The enzyme-catalyzed esterification can optionally be conducted in the presence of a diluent or solvent. Examples of suitable diluents or solvents are especially aliphatic hydrocarbons such as hexane, cyclohexane, heptane, octane; aromatic hydrocarbons, for example toluene, xylene; dialkyl ethers such as methyl tert-butyl ether and diisopropyl ether. Typically 1-5 equivalents of alcohol are used per equivalent of 3-(E) acid. The esterification is typically conducted at a temperature within a range from 0 to 80° C.

The lipase esterifies the 3-(E) acid of the formula (I-E) with alcohols very much more quickly than the corresponding 3-(Z) acid of the formula (I-Z). Therefore, a separable composition is obtained, comprising the 3-(E) ester, unconverted 3-(E) acid of the formula (I-E) and unconverted 3-(Z) acid of the formula (I-Z).

The composition obtained in step (1) can be separated by extraction or distillation.

In step (4), the 3-(E) ester isolated in step (2) is optionally subjected to an acid-, base- or enzyme-catalyzed ester cleavage to obtain the 3-(E) acid of the formula (I-E) or salt thereof. Since the compound of the formula (I-E) is frequently the product of value, it is appropriate to conduct the ester cleavage.

In a further preferred embodiment, the process of the invention for preparing an E/Z isomer mixture of the formula (I) comprises the following additional steps:

-   -   (i) the composition comprising the E/Z isomer mixture of the         formula (I) is subjected to an esterification in the presence of         an alcohol to obtain the 3-(E) ester and the 3-(Z) ester;     -   (ii) the 3-(E) ester and the 3-(Z) ester obtained in (i) are         subjected to a lipase-catalyzed enzymatic hydrolysis, wherein         the lipase at least partly cleaves the 3-(E) ester to give the         3-(E) acid of the formula (I-E) to obtain a composition         comprising the 3-(E) acid of the compound of the formula (I-E),         unconverted 3-(E) ester and unconverted 3-(Z) ester;     -   (iii) the composition obtained in (ii) is separated to obtain a         composition comprising the 3-(E) acid of the compound of the         formula (I-E) and to obtain a composition comprising unconverted         3-(E) ester and unconverted 3-(Z) ester;     -   (iv) the composition which is obtained in (iii) and comprises         unconverted 3-(E) ester and unconverted 3-(Z) ester is subjected         to an ester cleavage to obtain a composition depleted of 3-(E)         acid of the formula (I-E) or salt thereof and enriched in 3-(Z)         acid of the formula (I-Z) or salt thereof; and     -   (v) the composition which is obtained in (iv) and is depleted of         3-(E) acid of the formula (I-E) and enriched in 3-(Z) acid of         the formula (I-Z) is subjected to an isomerization to increase         the content of 3-(E) acid of the formula (I-E).

Preferably, the esterification in step (i) is effected with an aliphatic alcohol. Suitable aliphatic alcohols are C₁-C₂₀-alkanols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec butanol, n-pentanol, n-hexanol, n-heptanol and n-octanol. The esterification can be conducted under acid, base or enzyme catalysis. The esterification is typically conducted at a temperature within a range from 0 to 80° C.

Processes for enzymatically catalyzed ester cleavage of a mixture of 3-(E)-unsaturated carboxylic acid and 3-(Z)-unsaturated carboxylic acid in the presence of water are known, for example, from EP 17157974.1.

Many lipases are capable of catalyzing ester cleavages with high substrate selectivity. In step (ii), the composition obtained in step (i), in the presence of water and a lipase enzyme, is subjected to an enzyme-catalyzed ester cleavage to obtain a composition comprising 3-(E) acid of the formula (I-E), unconverted 3-(E) ester and unconverted 3-(Z) ester. The lipases are preferably Candida antarctica lipase (CALB) or a form immobilized on a polymeric carrier, such as Novozym 435®.

The composition obtained in step (ii) can be separated by distillation or extraction. This gives a composition comprising 3-(E) acid of the formula (I-E). Likewise obtained is a composition comprising the 3-(E) ester and 3-(Z) ester.

The ester cleavage in step (iv) can be effected under acid, base or enzyme catalysis. This gives a composition comprising 3-(E) acid of the formula (I-E) or salt thereof and 3-(Z) acid of the formula (I-Z) or salt thereof, with a reduced content of 3-(E) acid of the formula (I-E) and an increased content of 3-(Z) acid of the formula (I-Z) compared to the composition used in step (i).

In steps (3) and (v) of the aforementioned processes, the composition obtained is subjected to an isomerization of the 3-(Z) acid of the formula (I-Z) to the 3-(E) acid of the formula (I-E) in order to increase the proportion of product of value. The isomerization is preferably effected in the presence of an anhydride of an organic acid and a base. Suitable anhydrides are anhydrides of aliphatic C₁-C₁₂ monocarboxylic acids, anhydrides of aliphatic C₄-C₂₀ dicarboxylic acids, anhydrides of cycloaliphatic C₇-C₂₀ dicarboxylic acids, anhydrides of aromatic C₈-C₂₀ dicarboxylic acids, anhydrides of aliphatic sulfonic acids and anhydrides of aromatic sulfonic acids. Suitable bases are alkali metal carbonates, alkaline earth metal carbonates, alkali metal hydrogencarbonates, alkaline earth metal hydrogencarbonates, alkali metal phosphates, alkaline earth metal phosphates, amines, basic N-heteroaromatics, basic ion exchangers and mixtures thereof. The isomerization is preferably effected in the presence of an anhydride of an organic acid and a base. The process can advantageously be conducted at a temperature of 60 to 175° C., preferably 70 to 160° C.

The pressure is uncritical. Therefore, the isomerization can be conducted at elevated pressure, reduced pressure or atmospheric pressure. When using a base and/or an anhydride having a boiling point below the reaction temperature at standard pressure, the process is appropriately conducted in a pressure reactor. Advantageously, the isomerization can also be conducted under the conditions of the process of the invention. Advantageously, the presence of a transition metal catalyst is not required for the isomerization.

The compounds of the general formula (I) obtained by the process of the invention can be subjected to a reduction with conversion of the acid or ester group to the corresponding alcohols. In a specific embodiment, first of all, a mixture of (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid and (3Z,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid, obtainable as described above, is subjected to a separation to obtain (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid, for example as described above, and (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid to a reduction to obtain (3E,7E)-homofarnesol (VI)

(3E,7E)-Homofarnesol (VI) is likewise an important intermediate for preparation of aroma chemicals.

The invention further provides for the preparation of (−)-ambrox. The preparation can be effected by known methods proceeding from stereoisomerically pure (3E/7E)-homofarnesylic acid as shown in scheme 1 below.

Reference is made here in full to the disclosure of EP 16156410, WO 2010/139719 and WO 2012/066059, which describe the biocatalytic cyclization of unsaturated substrates, for example of terpene-like hydrocarbons, using cyclase enzymes.

Sclareolide (VII) can be obtained, for example, by cyclase-catalyzed conversion of (3E/7E)-homofarnesylic acid prepared in accordance with the invention. Sclareolide (VII) can then be reduced chemically, for example by reaction with LiAlH₄ or NaBH₄, to obtain ambrox-1,4-diol (see Mookherjee et al.; Perfumer and Flavourist (1990), 15: 27). Ambrox-1,4-diol can then be converted further to (−)-ambrox by known methods.

Hydrogenation catalysts which enable good selectivity with respect to the hydrogenation of the terminal carboxylic acid group to obtain the corresponding alcohol are likewise known to those skilled in the art. The hydrogenation and isomerization of the double bonds present in the compounds (I) can essentially be avoided.

Likewise known is the cyclization of (3E,7E)-homofarnesol to ambrox, there being descriptions both of enzymatic and chemical cyclizations. In this regard, reference is made to the disclosure of the following documents:

P. F. Vlad et al. Khimiya Geterotsiklicheskikh Soedinenii, Engl. Transl. 1991, 746 describe cyclization reactions using a superacid (fluorosulfonic acid in 2-nitropropane). A further suitable method comprises the enantioselective polyene cyclization of homofarnesyl triethylsilyl ether in the presence of O-(o-fluorobenzyl)binol and SnCl₄, as described by H. Yamamoto et al. J. Am. Chem. Soc. 2002, 3647.

Preference is given to biocatalytic cyclization as described in WO 2010/139719. According to this, the cyclization in step d1) is effected in the presence of a polypeptide having the activity of a homofarnesol-ambrox cyclase as enzyme.

For preparation of (−)-ambrox by this variant, homofarnesol is contacted and/or incubated with the homofarnesol-ambroxan cyclase and then the ambrox formed is isolated.

In one embodiment, homofarnesol is contacted with the homofarnesol-ambroxan cyclase in a medium and/or incubated therewith such that homofarnesol is converted to ambrox in the presence of the cyclase. Preferably, the medium is an aqueous reaction medium. The aqueous reaction media are preferably buffered solutions that generally have a pH of preferably 5 to 8. The buffer used may be a citrate, phosphate, TRIS (tris(hydroxymethyl)aminomethane) or MES (2-(N-morpholino)ethanesulfonic acid) buffer. In addition, the reaction medium may comprise further additives, for example detergents (for example taurodeoxycholate).

The homofarnesol is preferably used in the enzymatic reaction in a concentration of 5 to 100 mM, more preferably of 15 to 25 mM. This reaction can be conducted continuously or batchwise.

The enzymatic cyclization is appropriately effected at a reaction temperature below the deactivation temperature of the cyclase used. The reaction temperature in step d1) is preferably within a range from −10 to 100° C., more preferably from 0 to 80° C., particularly from 15 to 60° C. and especially from 20 to 40° C.

The ambrox reaction product can be extracted with organic solvents and optionally distilled for purification. Suitable solvents are specified hereinafter.

As well as monophasic aqueous systems, it is also possible to use biphasic systems. In this variant, it is possible to enrich the ambrox formed in the nonaqueous phase in order to isolate it. The second phase here is preferably selected from ionic liquids and organic water-immiscible solvents. After the reaction, ambrox in the organic phase is easily separable from the aqueous phase comprising the biocatalyst. Nonaqueous reaction media are understood to mean reaction media comprising less than 1% by weight and preferably less than 0.5% by weight of water, based on the total weight of the liquid reaction medium. More particularly, the reaction can be conducted in an organic solvent. Suitable organic solvents are, for example, aliphatic hydrocarbons preferably having 5 to 8 carbon atoms, such as pentane, cyclopentane, hexane, cyclohexane, heptane, octane or cyclooctane, halogenated aliphatic hydrocarbons, preferably having one or two carbon atoms, such as dichloromethane, chloroform, carbon tetrachloride, dichloroethane or tetrachloroethane, aromatic hydrocarbons such as benzene, toluene, the xylenes, chlorobenzene or dichlorobenzene, aliphatic acyclic and cyclic ethers or alcohols, preferably having 4 to 8 carbon atoms, such as ethanol, isopropanol, diethyl ether, methyl tert-butyl ether, ethyl tert-butyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, tetrahydrofuran, or esters such as ethyl acetate or n-butyl acetate, or ketones such as methyl isobutyl ketone or dioxane or mixtures thereof. Particular preference is given to using the aforementioned heptane, methyl tert-butyl ether, diisopropyl ether, tetrahydrofuran, ethyl acetate.

Suitable enzymes are described in WO 2010/139719, which is incorporated here by reference in full. According to this, the enzyme is a polypeptide encoded by a nucleic acid molecule comprising at least one nucleic acid molecule selected from:

a) nucleic acid molecule which codes for a polypeptide comprising SEQ ID NO 2, 5, 6, 7, 8, 9, 10 or 11; b) nucleic acid molecule which comprises at least one polynucleotide of the sequence shown in SEQ ID NO 1; c) nucleic acid molecule which codes for a polypeptide whose sequence has an identity of at least 46% to the sequences SEQ ID NO 2, 5, 6, 7, 8, 9, 10 or 11; d) nucleic acid molecule according to (a) to (c) which is a functionally equivalent polypeptide or a fragment of the sequence according to SEQ ID NO 2, 5, 6, 7, 8, 9, 10 or 11; e) nucleic acid molecule coding for a functionally equivalent polypeptide with the activity of a homofarnesol-ambroxan cyclase which is obtained by amplifying a nucleic acid molecule from a cDNA bank or from genomic DNA by means of the primer according to sequence No. 3 and 4, or chemically synthesizing the nucleic acid molecule by de novo synthesis; f) nucleic acid molecule coding for a functionally equivalent polypeptide with the activity of a homofarnesol-ambroxan cyclase which hybridizes under stringent conditions with a nucleic acid molecule according to (a) to (c); g) nucleic acid molecule coding for a functionally equivalent polypeptide with the activity of a homofarnesol-ambroxan cyclase which can be isolated from a DNA bank using a nucleic acid molecule according to (a) to (c) or fragments thereof of at least 15 nt, preferably 20 nt, 30 nt, 50 nt, 100 nt, 200 nt or 500 nt as probe under stringent hybridization conditions; and h) nucleic acid molecule coding for a functionally equivalent polypeptide with the activity of a homofarnesol-ambroxan cyclase, where the sequence of the polypeptide has an identity of at least 46% to the sequences SEQ ID NO 2, 5, 6, 7, 8, 9, 10 or 11; i) nucleic acid molecule coding for a functionally equivalent polypeptide with the activity of a homofarnesol-ambroxan cyclase, where the polypeptide is encoded by a nucleic acid molecule selected from the group of those described in a) to h) and has been isolated, or can be isolated, by means of a monoclonal antibody; j) nucleic acid molecule coding for a functionally equivalent polypeptide with the activity of a homofarnesol-ambroxan cyclase, where the polypeptide has an analogous or similar binding site to a polypeptide encoded by a nucleic acid molecule selected from the group of those described in a) to h).

In spite of a multitude of existing aroma chemicals (fragrances and flavorings) and processes for preparation thereof, there is a constant need for novel components in order to be able to satisfy the multitude of properties desired for the extremely diverse fields of use and for simple synthesis routes in order to make them available. The process of the invention enables the effective preparation of compounds of the general formula (I) that can serve as synthesis units of interest in the provision of novel and already known aroma chemicals, such as (−)-ambrox. After hydrogenation of the acid function, it is possible to obtain alcohols which may in turn be synthesis units of interest and be suitable for use as surfactant alcohols

The invention is elucidated in detail by the working examples which follow. The examples which follow demonstrate that the invention can be conducted advantageously with different reactants and transition metal catalysts.

Abbreviations

Ac₂O represents acetic anhydride; DMAP stands for 4-(dimethylamino)pyridine; eq. stands for equivalent(s); Fe(acac)₃ represents tris(acetylacetonato)iron(III); area % stands for area percent; GC stands for gas chromatography; [Ir(COD)Cl]₂ represents bis(1,5-cyclooctadiene)diiridium(I) dichloride; MTBE stands for methyl tert-butyl ether; NEt₃ represents triethylamine; org. stands for organic; P(Cy)₃ represents tricyclohexylphosphine; Pd(acac)₂ represents bis(acetylacetonato)palladium(II); Pd(dba)₂ represents bis(dibenzylideneacetone)palladium(0); Pd(OAc)₂ represents palladium(II) acetate; Rh(CO)₂(acac) represents (acetylacetonato)dicarbonylrhodium(I); Ru(acac)₃ represents tris(acetylacetonato)ruthenium(III); Acid sel. stands for acid selectivity; THF stands for tetrahydrofuran; TPP stands for triphenylphosphine; rpm stands for revolutions per minute.

The products were identified with the aid of GC, ¹H NMR and ¹³C NMR analysis. The workup of the reaction mixtures was not optimized.

Example 1: Pd-Catalyzed Carbonylation Proceeding from Linalool

Palladium(II) acetate (19 mg, 0.085 mmol), triphenylphosphine (51 mg, 0.195 mmol) and DMAP (49 mg, 0.4 mmol) were initially charged in a glass autoclave under argon. Linalool (10.8 g, 70 mmol), triethylamine (6.9 g, 68 mmol) and acetic anhydride (2 g, 20 mmol) were added in an argon counterflow. Subsequently, 10 bar CO was applied and the mixture was stirred at 1000 rpm at this pressure and at internal temperature 60° C. for 24 h. Thereafter, the mixture was cooled to room temperature and decompressed. GC analysis of the reaction output gave a conversion of 94% with a selectivity for the E/Z-4,8-dimethyl-3,7-nonadienoic acid target product of 62%.

After the reaction had ended, MTBE (25 mL) and aqueous NaOH (5%, 70 mL) were added. The phases were separated and the aqueous phase was washed with MTBE (2×50 mL). The aqueous phase was brought to pH=1 with H₂SO₄ (20%) and extracted with MTBE (3×50 mL). The organic phases from the acidic extraction were combined, washed to neutrality with water (3×70 mL) and dried over MgSO₄. After concentration, 7.1 g (56%) of E/Z-4,8-dimethyl-3,7-nonadienoic acid were obtained with an E/Z ratio of 55:45 (¹H NMR). The NMR data correspond to the data of Snyder et al. Angew. Chem., 121, 2009, 8039. ¹³C NMR (CDCl₃), E-homomyrcenylcarboxylic acid: 179.9, 139.5, 131.7, 125.1, 116.2, 40.2, 34.0, 27.2, 26.2, 18.0, 16.6; Z-homomyrcenylcarboxylic acid: 179.9, 139.5, 132.1, 124.8, 117.0, 34.0, 32.6, 27.0, 26.2, 23.7, 18.0.

Examples 1.1-1.12: Pd-Catalyzed Carbonylation Proceeding from Linalool

Example 1 was repeated. The feedstocks for carbonylation of linalool, the conversion after 24 h and the selectivity for the E/Z-4,8-dimethyl-3,7-nonadienoic acid target product are reported in table I.

TABLE I Carbonylation of linalool Transition metal compound/ TPP DMAP Ac₂O CO Conversion Acid sel. Example (mol %) (mol %) (mol %) (mol %) (bar) after 24 h (GC area %) 1 Pd(OAc)₂/0.12 0.28 0.6 28 10 94% 62 1.1^(a)) Pd(OAc)₂/0.12 0.28 0.6 28 10 56% 79 1.2^(b)) Pd(OAc)₂/0.12 0.28 0.6 28 10 27% 66 1.3^(c)) Pd(OAc)₂/0.12 0.28 0.6 28 10 41% 47 1.4^(d)) Pd(OAc)₂/0.12 0.28 0.6 28 10 30% 50 1.5 Pd(acac)₂/0.12 0.28 0.6 28 10 80% 70 1.6 Pd(dba)₂/0.12 0.28 0.6 28 10 75% 60 1.7^(e)) PdCl₂/0.15 0.28 0.3 28 10 69% 58 1.8^(f)) Pd(OAc)₂/0.12 0.28 0.3 28 10 40% 44 1.9^(e)) Pd(OAc)₂/0.12 0.28 0.3 28 10 77% 63 1.10 PdCl₂/0.15 0.28 — — 10  0% — 1.11^(f)) PdCl₂/0.15 0.28 — — 10 14%  6 1.12^(f)) Pd(OAc)₂/0.12 0.28 — — 10  3% — ^(a))addition of 10 mL of pyridine rather than NEt₃; ^(b))addition of 10 mL of THF rather than NEt₃; ^(c))addition of 10 mL of toluene rather than NEt₃; ^(d))addition of 10 mL of dioxane rather than NEt₃; ^(e))80° C. rather than 60° C.; ^(f))addition of 10 mL of THF rather than NEt₃, 100° C. rather than 60° C.; ^(g))addition of 10 mL of THF rather than NEt₃, 80° C. rather than 60° C.

Comparative example 1.10 shows that no conversion was achieved at 10 bar under the conditions of EP 0146859 (PdCl₂/TPP) in the absence of an anhydride source, and even at 100° C. very small conversions at most to the target product (comparative example 1.11). Comparative example 1.12 shows that only a minimal conversion was achieved in the case of use of Pd(OAc)₂ in the absence of an anhydride source.

Examples 1.13-1.17: Carbonylation Proceeding from Linalool Using Transition Metal Catalysts of Groups 8 and 9 of the Periodic Table

Example 1 was repeated. The feedstocks for carbonylation of linalool, the conversion after 24 h and the selectivity for the target product (E/Z-4,8-dimethyl-3,7-nonadienoic acid) are reported in table II.

TABLE II Carbonylation of linalool Transition metal Transition metal TPP/DMAP Ac₂O CO Conversion Acid sel. Example compound (mol %) (mol %) (mol %) (bar) after 24 h (GC area %) 1.13 Ru(acac)₃ 0.12 0.28/0.3 28 10 56% 60 1.14 Ru₃(CO)₁₂ 0.04 0.28/0.3 28 10 47% 31 1.15 Rh(CO)₂(acac) 0 12 0.28/0.3 28 10 58% 49 1.16 Fe(acac)₂ 0.12 0.28/0.3 28 10 36% 49 1.17 [Ir(COD)Cl]₂ 0.06 0.28/0.3 28 10 49% 27

Example 2: Carbonylation of 3-methyl-1-penten-3-ol

Palladium(II) acetate (22 mg, 0.1 mmol), triphenylphosphine (52 mg, 0.2 mmol) and DMAP (49 mg, 0.4 mmol) were initially charged in a glass autoclave under argon. 3-Methyl-1-penten-3-ol (6.7 g, 67 mmol), triethylamine (6.7 g, 67 mmol) and acetic anhydride (2 g, 20 mmol) were added in an argon counterflow. Subsequently, 10 bar CO was applied and the mixture was stirred at 1000 rpm at this pressure and at internal temperature 60° C. for 24 h. Thereafter, the mixture was cooled to room temperature and decompressed. GC analysis of the reaction output gave a conversion of 70% with a selectivity for the E/Z-(4-methyl)-3-hexenoic acid target product of 75%.

After the reaction had ended, MTBE (25 mL) and aqueous NaOH (5%, 50 mL) were added. The phases were separated and the aqueous phase was washed with MTBE (2×25 mL). The aqueous phase was brought to pH=1 with H₂SO₄ (20%) and extracted with MTBE (3×25 mL). The organic phases from the acidic extraction were combined, washed to neutrality with water (5×25 mL) and dried over MgSO₄. After concentration, 2.3 g (27%) of E/Z-(4-methyl)-3-hexenoic acid were obtained as a pale yellow oil with an E/Z ratio of 3:2 (¹H NMR). ¹³C NMR (d₈-toluene); E-(4-methyl)-3-hexenoic acid: 179.7, 140.8, 114.5, 33.7, 32.5, 16.1, 12.6; Z-(4-methyl)-3-hexenoic acid: 179.7, 141.1, 115.5, 33.4, 25.2, 22.8, 12.6.

Example 3: Carbonylation of 1-hepten-3-ol

Palladium(II) acetate (22 mg, 0.1 mmol), triphenylphosphine (52 mg, 0.22 mmol) and DMAP (55 mg, 0.45 mmol) were initially charged in a glass autoclave under argon. 1-Hepten-3-ol (7.6 g, 66 mmol), triethylamine (6.7 g, 67 mmol) and acetic anhydride (1.8 g, 17 mmol) were added in an argon counterflow. Subsequently, 10 bar CO was applied and the mixture was stirred at 1000 rpm at this pressure and at internal temperature 60° C. for 24 h. Thereafter, the mixture was cooled to room temperature and decompressed. GC analysis of the reaction output gave a conversion of 75% with a selectivity for the E/Z-3-octenoic acid target product of 50%.

After the reaction had ended, MTBE (25 mL) and aqueous NaOH (5%, 50 mL) were added. The phases were separated and the aqueous phase was washed with MTBE (2×50 mL). The aqueous phase was brought to pH=1 with H₂SO₄ (about 20 mL, 20%) and extracted with MTBE (3×50 mL). The organic phases from the acidic extraction were combined, washed to neutrality with water (4×50 mL) and dried over MgSO₄. After concentration, 2.4 g (26%) of E/Z-3-octenoic acid with an E/Z ratio of 78:22 (¹H NMR) were obtained. The NMR data correspond to the data from Wirth et al. Org. Lett., 9, 2007, 3169. ¹³C NMR (d_(e)-toluene), E-3-octenoic acid: 179.4, 135.0, 121.4, 38.0, 32.5, 31.6, 22.6, 14.1.

Example 4: Carbonylation of E-nerolidol

Palladium(II) acetate (46 mg, 0.2 mmol), triphenylphosphine (120 mg, 0.46 mmol) and DMAP (56 mg, 0.46 mmol) were initially charged in a steel autoclave under argon. E-nerolidol (34 g, 152.6 mmol), triethylamine (17 g, 167 mmol) and acetic anhydride (3.6 g, 35 mmol) were added in an argon counterflow. Subsequently, 10 bar CO was applied and the mixture was stirred at 1000 rpm at this pressure and at internal temperature 70° C. for 24 h. After 24 h, the mixture was cooled to room temperature and decompressed. GC analysis of the reaction output gave a conversion of 95% with a selectivity for the E/Z-homofarnesylic acid target product of 81%.

After the reaction had ended, the crude product was purified by Kugelrohr distillation (1 mbar, to 170° C.). This gave 23 g (61%) of E/Z-homofarnesylic acid with a purity (GC) of 97% with an isomer ratio of E-homofarnesylic acid:Z-homofarnesylic acid of 64:36 (GC).

¹³C NMR (CDCl₃): E-homofarnesylic acid: 179.1, 139.8, 135.4, 131.4, 124.4, 123.8, 114.9, 33.6, 39.8, 39.6, 26.8, 25.8, 26.4, 17.8, 16.5, 16.1; Z-homofarnesylic acid: 179.2, 139.7, 135.7, 131.2, 124.5, 123.7, 115.9, 39.8, 33.5, 32.2, 26.8, 26.3, 25.7, 23.4, 17.7, 16.0.

Example 4 was repeated. The feedstocks for carbonylation of E-nerolidol, conversion after 24 h and 6 h and the yield of E/Z-homofarnesylic acid target product (sum of the two isomers) are reported in table Ill.

TABLE III Carbonylation of E-nerolidol Conversion (Pd(OAc)₂ TPP DMAP Ac₂O CO after 24 h/ (Yield^(#) Example (mol %) (mol %) (mol %) (mol %) (bar) (6 h) (GC area %) 4 0.13 0.3 0.3 23 10 95%/(65%) 77% 4.1 0.13 0.3 — — 10  0% — 4.2 0.13 1.3 0.3 23 10 50% 33% 4.3 0.13 — 0.3 23 10 26%  1% 4.4 0.13 0.3 0.3 — 10  0% — 4.5 0.13 0.3 — 23 10 94%/(54%) 77% 4.6^(a)) 0.13 0.3 0.3 23 10 70% 54% 4.7 0.13 0.3 0.3 ^(b)) 10 52% 32% 4.8 0.13 0.3 0.3 ^(c)) 10 >99%  95% 4.9 0.13 0.3 — ^(d)) 10 >99%  58% 4.10^(e)) 0.13 0.3 0.3 23 10 34% 16% 4.11^(f)) 0.13 0.3 0.3 23 10 30% 18% 4.12 0.13 ^(g)) 0.3 23 10 76% 58% 4.13 0.13 ^(h)) 0.3 23 10 83% 72% 4.14 0.13 0.3 0.3 23 20 99% 85% 4.15 0.13 0.3 0.3 23 40 97% 85% 4.16 0.13 0.3 0.3 23 80 94% 79% 4.17 0.13 ^(i)) 0.3 23 20 93% 72% 4.18 0.13 ^(k)) 0.3 23 20 95% 80% 4.19 0.13 0.3 0.3 16 20 93% 79% ^(a))half the amount of NEt₃; ^(b)) 23 mol % of allyl acetate (CAS 591-87-7) rather than Ac₂O; ^(c)) 30 mol % of E-nerolidyl acetate rather than Ac₂O; ^(d)) 30 mol % of E-nerolidyl acetate rather than Ac₂O; ^(e))120° C.; ^(f))THF in place of NEt₃; ^(g)) 0.3 mol % of P(Cy)₃ rather than TPP; ^(h)) 0.3 mol % of tri(p-tolyl)phosphine rather than TPP; ^(i)) 0.3 mol % of di(tert-butyl)phenylphosphine rather than TPP; ^(k)) 0.3 mol % of cyclohexyldiphenylphosphine rather than TPP; ^(#)yield determined via GC area % as product of selectivity and conversion

Example 5: Carbonylation of E-nerolidyl Acetate

Palladium(II) acetate (50 mg, 0.22 mmol), triphenylphosphine (130 mg, 0.5 mmol) and DMAP (70 mg, 0.57 mmol) were initially charged in a steel autoclave under argon. E-Nerolidyl acetate (42.5 g, 142 mmol), triethylamine (9 g, 89 mmol) and water (2.8 g, 156 mmol) were added in an argon counterflow. Subsequently, 10 bar CO was applied and the mixture was stirred at 1000 rpm at this pressure and at internal temperature 70° C. for 24 h. Thereafter, the mixture was cooled to room temperature and decompressed. GC analysis of the reaction output gave a conversion of 97% with a selectivity for E/Z-homofarnesylic acid of 71%. Ratio of E-homofarnesylic acid:Z-homofarnesylic acid=64:36 (GC).

Example 5 was repeated. The feedstocks for carbonylation of E-nerolidyl acetate, conversion after 4 h and 24 h and the yield of the E/Z-homofarnesylic acid target product (sum of the two isomers) are reported in table IV.

TABLE IV Carbonylation of E-nerolidyl acetate Conversion GC yield Pd(OAc)₂ TPP DMAP H₂O CO after 24 h of acid Example (mol %) (mol %) (mol %) (eq.) (bar) (4 h) (area %) Notes 5 0.15 0.4 0.4 1.1 10  97% (93%) 74% 70° C. 5.1 0.13 0.3 0.3 1.1 10 >99% (65%) 69% 70° C., THF rather than NEt₃ 5.2 0.13 0.3 0.3 — 10 >99% <20%  70° C. 5.3 0.13 0.3 — 1.1 10 >99% 86% 70° C. 5.4 0.13 0.3 — 1.0 10  97% 84% 50° C.

Example 6: Carbonylation of 1-vinylcyclohexanol

Palladium(II) acetate (22 mg, 0.1 mmol), triphenylphosphine (54 mg, 0.21 mmol) and DMAP (50 mg, 0.41 mmol) were initially charged in a glass autoclave under argon. 1-Vinylcyclohexanol (8.35 g, 66 mmol), triethylamine (6.7 g, 67 mmol) and acetic anhydride (1.8 g, 17 mmol) were added in an argon counterflow and 10 bar CO was applied. The mixture was stirred at 1000 rpm at internal temperature 60° C. for 20 h, the pressure was kept at 10 bar, and after 48 h the mixture was cooled to room temperature and decompressed. GC conversion: 54%; selectivity for 3-cyclohexylidenepropanoic acid: 63%.

After the reaction had ended, MTBE (25 mL) and aqueous NaOH (5%, 50 mL) were added. The phases were separated and the aqueous phase was washed with MTBE (2×50 mL). The aqueous phase was brought to pH=1 with H₂SO₄ (about 30 mL, 20%) and extracted with MTBE (3×50 mL). The organic phases from the acidic extraction were combined, washed to neutrality with water (4×50 mL) and dried over MgSO₄. Concentration gave 3.1 g (31%) of 3-cyclohexylidenepropanoic acid. ¹³C NMR (d₆-toluene): 180.0, 143.8, 112.9, 37.5, 33.3, 29.4, 29.0, 28.1, 27.4.

Example 7: Isomer Separation of a Composition Comprising E/Z-Homofarnesylic Acid and Isomerization for Enrichment of the E-Homofarnesylic Acid

Isomer Separation:

The mixture obtained in example 4 was dissolved in n-heptane (100 g), isopropanol (10 g) and Novozym 435 (0.5 g) were added and the mixture was stirred at 60° C. for about 17 h. The enzyme was then filtered off. At a temperature of 0° C., methanol and water were added, and the pH of the reaction mixture was adjusted to 12-13 at a temperature below 10° C. by adding aqueous NaOH. The phases were separated, giving an organic phase comprising (3E,7E)-homofarnesylic acid isopropyl ester as the main component and an aqueous phase having a composition that comprised 3Z,7E-homofarnesylic acid:3E,7E-homofarnesylic acid:2E,7E-homofarnesylic acid:further compounds in a ratio of 68%:14%:17%:1% (HPLC).

Isomerization:

Palladium(II) acetate (22 mg, 0.098 mmol), triphenylphosphine (58 mg, 0.22 mmol) and DMAP (25 mg, 0.2 mmol) were initially charged under argon in a steel autoclave. The acid mixture of 3Z,7E-homofarnesylic acid:3E,7E-homofarnesylic acid:2E,7E-homofarnesylic acid:further compounds (in a ratio of 68%:14%:17%:1%) (17.5 g, 51 mmol), triethylamine (8.1 g, 80 mmol) and acetic anhydride (1.7 g, 17 mmol) were added in an opposing flow of argon, and CO was injected to 20 bar. Subsequently, the mixture was stirred at internal temperature 140° C. for 14 h (1000 rpm). In the course of this, the pressure was maintained at 20 bar. This was followed by cooling to room temperature and decompression. This gave a composition that comprised 3Z,7E-homofarnesylic acid:3E,7E-homofarnesylic acid:2E,7E-homofarnesylic acid:further compounds in a ratio of 22%:33%:21%:24% (HPLC). 

The invention claimed is:
 1. A process for preparing a composition comprising at least one unsaturated carboxylic acid of the general formula (I)

or a salt thereof, in which R¹ is hydrogen, linear or branched C₁-C₂₄-alkyl, linear or branched C₂-C₂₄-alkenyl having 1, 2, 3 or more than 3 C—C double bonds, unsubstituted C₅-C₁₂-cycloalkyl or C₅-C₁₂-cycloalkyl substituted by 1, 2 or 3 C₁-C₆-alkyl radicals or unsubstituted aryl or aryl substituted by 1, 2 or 3 C₁-C₆-alkyl radicals, R² is hydrogen, linear or branched C₁-C₂₄-alkyl or linear or branched C₂-C₂₄-alkenyl having 1, 2, 3 or more than 3 C—C double bonds, or R¹ and R² together with the carbon atom to which they are bonded are unsubstituted C₅-C₇-cycloalkyl or are C₅-C₇-cycloalkyl bearing 1, 2 or 3 linear or branched C₁-C₆-alkyl radicals, in which an allyl alcohol selected from compounds of the general formulae (II.1) and (II.2)

is subjected to a carbonylation by reaction with carbon monoxide in the presence of a transition metal catalyst comprising at least one metal of groups 8, 9 and 10 of the Periodic Table of the Elements, wherein the reaction is additionally effected in the presence of at least one organic phosphorus compound as ligand and in the presence of a substoichiometric amount, based on the allyl alcohol, of a compound A) selected from anhydrides of aliphatic C₁-C₁₂-monocarboxylic acids, anhydrides of aliphatic C₄-C₂₀-dicarboxylic acids, anhydrides of cycloaliphatic C₇-C₂₀-dicarboxylic acids, anhydrides of aromatic C₈-C₂₀-dicarboxylic acids and acylated allyl alcohols of the formulae (III.1) and (III.2)

in which R³ is hydrogen, linear or branched C₁-C₂₄-alkyl, linear or branched C₂-C₂₄-alkenyl having 1, 2, 3 or more than 3 C—C double bonds, unsubstituted C₅-C₁₂-cycloalkyl or C₅-C₁₂-cycloalkyl substituted by 1, 2 or 3 C₁-C₆-alkyl radicals or unsubstituted aryl or aryl substituted by 1, 2 or 3 C₁-C₆-alkyl radicals, R⁴ is hydrogen, linear or branched C₁-C₂₄-alkyl or linear or branched C₂-C₂₄-alkenyl having 1, 2, 3 or more than 3 C—C double bonds, or R³ and R⁴ together with the carbon atom to which they are bonded are unsubstituted C₅-C₇-cycloalkyl or are C₅-C₇-cycloalkyl bearing 1, 2 or 3 linear or branched C₁-C₆-alkyl radicals, R⁵ is C₁-C₅-alkyl, and wherein the reaction is effected at a temperature of not more than 100° C.
 2. A process for preparing a composition comprising at least one unsaturated carboxylic acid of the general formula (I)

or a salt thereof, in which R¹ is hydrogen, linear or branched C₁-C₂₄-alkyl, linear or branched C₂-C₂₄-alkenyl having 1, 2, 3 or more than 3 C—C double bonds, unsubstituted C₅-C₁₂-cycloalkyl or C₅-C₁₂-cycloalkyl substituted by 1, 2 or 3 C₁-C₆-alkyl radicals or unsubstituted aryl or aryl substituted by 1, 2 or 3 C₁-C₆-alkyl radicals, R² is hydrogen, linear or branched C₁-C₂₄-alkyl or linear or branched C₂-C₂₄-alkenyl having 1, 2, 3 or more than 3 C—C double bonds, or R¹ and R² together with the carbon atom to which they are bonded are unsubstituted C₅-C₇-cycloalkyl or are C₅-C₇-cycloalkyl bearing 1, 2 or 3 linear or branched C₁-C₆-alkyl radicals, in which an acylated allyl alcohol selected from compounds of the general formulae (IV.1) and (IV.2)

in which R⁶ is C₁-C₅-alkyl, is subjected to a carbonylation by reaction with carbon monoxide in the presence of a transition metal catalyst comprising at least one metal of groups 8, 9 and 10 of the Periodic Table of the Elements, wherein the reaction is additionally effected in the presence of at least one organic phosphorus compound as ligand and in the presence of water and wherein the reaction is effected at a temperature of not more than 100° C., wherein the carbonylation is not effected in the presence of an added hydrohalic acid and not in the presence of an added alkali metal halide, alkaline earth metal halide or ammonium halide; and wherein the reaction mixture of the carbonylation has a halide content of not more than 2 mol %, based on the total content of allyl alcohol of the general formulae (IV.1) and (IV.2).
 3. The process according to claim 1, wherein the reaction is effected at a pressure of not more than 30 bar.
 4. The process according to claim 1, wherein the carbonylation is not effected in the presence of an added hydrohalic acid and not in the presence of an added alkali metal halide, alkaline earth metal halide or ammonium halide.
 5. The process according to claim 1, wherein the reaction mixture of the carbonylation has a halide content of not more than 2 mol % based on the total content of allyl alcohol of the general formulae (II.1) and (II.2).
 6. The process according to claim 1, wherein the compound A) is selected from acetic anhydride and allyl acetate.
 7. The process according to claim 1, wherein the compound A) used is an ester of the formula (III.1) or (III.2) that derives from the alcohol of the formula (II.1) or (II.2) used as the reactant for carbonylation.
 8. The process according to claim 1, in which the reaction is additionally effected in the presence of a nucleophilic reagent selected from 4-(di(C₁-C₄-alkyl)amino)pyridine, 4-(C₁-C₄-alkyl)pyridine and 4-(1-pyrrolidinyl)pyridine.
 9. The process according to claim 8, in which the nucleophilic reagent selected from 4-(di(C₁-C₄-alkyl)amino)pyridine, 4-(C₁-C₄-alkyl)pyridine and 4-(1-pyrrolidinyl)pyridine, is used in an amount of 0.01 to 5 mol %, based on the total molar amount of the compounds (II.1) and (II.2).
 10. The process according to claim 1, in which the transition metal is used for the reaction in an amount of not more than 0.5 mol %, based on the total molar C amount of the compounds (II.1) and (II.2).
 11. The process according to claim 1, wherein the transition metal is selected from Pd, Ru, Rh, Ir and Fe.
 12. The process according to claim 1, wherein the organic phosphorus compound is selected from trialkylphosphines, triarylphosphines, dialkylarylphosphines, alkyldiarylphosphines, cycloalkyldiarylphosphines, dicycloalkylarylphosphines, tricycloalkyl-phosphines, triheterocyclylphosphines and trihetarylphosphines.
 13. The process according to claim 1, in which the total amount of the compound A) is not more than 50 mol %, based on the total molar amount of the compound (II.1) and (II.2).
 14. The process according to claim 8, in which the reaction is additionally effected in the presence of a base other than the nucleophilic reagent selected from 4-(dimethylamino)-pyridine, 4-(C₁-C₄-alkyl)pyridine and 4-(1-pyrrolidinyl)pyridine.
 15. The process according to claim 1, in which the reaction is effected in the presence of an added aprotic organic solvent.
 16. The process according to claim 1, wherein the reaction is effected at a temperature of not more than 80° C.
 17. The process according to claim 1, wherein the reaction is effected at a pressure of not more than 25 bar.
 18. The process according to claim 1, wherein the compound of the general formula (II.1) which is used for the reaction is selected from nerolidol, linalool, 3-methyl-1-penten-3-ol, 1-hepten-3-ol and 1-vinylcyclohexanol.
 19. The process according to claim 1, wherein E-nerolidol is used for the reaction.
 20. The process according to claim 1, in which E-nerolidol is subjected to a carbonylation, giving a reaction mixture comprising (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid or a salt thereof and (3Z,7E)-4,8,12-trimethyl-trideca-3,7,11-trienoic acid or a salt thereof in a weight ratio of 80:20 to 50:50.
 21. The process according to claim 1, wherein the compound of the general formula (II.2) used for the reaction is farnesol.
 22. The process according to claim 1, wherein the composition comprising the at least one unsaturated carboxylic acid of the formula (I) is an E/Z isomer mixture of the formula (I) comprising a 3-(E) acid of the formula (I-E) and a 3-(Z) acid of the formula (I-Z)

in which R¹ and R² have different definitions and R¹ has a higher priority according to IUPAC; and this E/Z isomer mixture of the formula (I) is subjected to an enrichment of one isomer.
 23. The process according to claim 22, wherein the composition comprising the at least one unsaturated carboxylic acid of the formula (I) is an E/Z isomer mixture of the formula (I) comprising a 3-(E) acid of the formula (I-E) and a 3-(Z) acid of the formula (I-Z), in which, in addition, (1) the composition comprising the E/Z isomer mixture of the formula (1), in the presence of an alcohol and of a lipase enzyme, is subjected to an enzyme-catalyzed esterification, wherein the 3-(E) acid of the formula (I-E) is converted at least partly to a 3-(E) ester, so as to obtain a composition comprising the 3-(E) ester, unconverted 3-(E) acid of the formula (I-E) and unconverted 3-(Z) acid of the formula (I-Z); (2) the composition obtained in (1) is separated to obtain a composition depleted of 3-(E) acid of the formula (I-E) and enriched in 3-(Z) acid of the formula (I-Z), and to obtain a composition comprising the 3-(E) ester; (3) the composition obtained in (2) which is depleted of 3-(E) acid of the formula (I-E) and enriched in 3-(Z) acid of the formula (I-Z) is subjected to an isomerization to increase the content of 3-(E) acid of the formula (I-E); and (4) optionally, the 3-(E) ester obtained in (2) is cleaved to obtain the 3-(E) acid of the formula (I-E).
 24. The process according to claim 22, wherein the composition comprising the at least one unsaturated carboxylic acid of the formula (I) is an E/Z isomer mixture of the formula (I) comprising a 3-(E) acid of the formula (I-E) and a 3-(Z) acid of the formula (I-Z), in which, in addition, (i) the composition comprising the E/Z isomer mixture of the formula (I) is subjected to an esterification in the presence of an alcohol to obtain the 3-(E) ester and the 3-(Z) ester; (ii) the 3-(E) ester and the 3-(Z) ester obtained in (i) are subjected to a lipase-catalyzed enzymatic hydrolysis, wherein the lipase at least partly cleaves the 3-(E) ester to give the 3-(E) acid of the formula (I-E) to obtain a composition comprising the 3-(E) acid of the compound of the formula (I-E), unconverted 3-(E) ester and unconverted 3-(Z) ester; (iii) the composition obtained in (ii) is separated to obtain a composition comprising the 3-(E) acid of the compound of the formula (I-E) and to obtain a composition comprising unconverted 3-(E) ester and unconverted 3-(Z) ester; (iv) the composition which is obtained in (iii) and comprises unconverted 3-(E) ester and unconverted 3-(Z) ester is subjected to an ester cleavage to obtain a composition depleted of 3-(E) acid of the formula (I-E) or salt thereof and enriched in 3-(Z) acid of the formula (I-Z) or salt thereof; and (v) the composition which is obtained in (iv) and is depleted of 3-(E) acid of the formula (I-E) and enriched in 3-(Z) acid of the formula (I-Z) is subjected to an isomerization to increase the content of 3-(E) acid of the formula (I-E).
 25. The process according to claim 23, wherein the isomerization to increase the content of 3-(E) acid of the formula (I-E) is effected in the presence of an anhydride of an organic acid and a base.
 26. A process for preparing (−)-ambrox (VIII)

in which a1) a mixture of (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid and (3Z,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid obtainable by the process as defined in claim 1; b1) the mixture of (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid and (3Z,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid is subjected to a separation to obtain (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid; c1) the (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid is subjected to a reduction to obtain (3E,7E)-homofarnesol (VI); d1) the (3E,7E)-homofarnesol (VI) is subjected to a cyclization to obtain (−)-ambrox (VIII); or a2) a mixture of (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid and (3Z,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid obtainable by the process as defined in claim 1; b2) the mixture of (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid and (3Z,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid is subjected to a separation to obtain (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid; c2) the (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid is subjected to a cyclization to obtain sclareolide (VII); d2) the sclareolide (VII) is subjected to a reduction to obtain (−)-ambrox (VIII).
 27. The process according to claim 1, wherein the reaction mixture of the carbonylation has a halide content of not more than 1 mol %, based on the total content of allyl alcohol of the general formulae (II.1) and (II.2).
 28. The process according to claim 2, wherein the reaction mixture of the carbonylation has a halide content of not more than 1 mol %, based on the total content of esters of the general formulae (IV.1) and (IV.2).
 29. The process according to claim 2, wherein the reaction is effected at a pressure of not more than 30 bar.
 30. The process according to claim 2, in which the transition metal is used for the reaction in an amount of not more than 0.5 mol %, based on the total molar amount of the compounds (IV.1) and (IV.2).
 31. The process according to claim 2, wherein the transition metal is selected from Pd, Ru, Rh, Jr and Fe.
 32. The process according to claim 2, wherein the organic phosphorus compound is selected from trialkylphosphines, triarylphosphines, dialkylarylphosphines, alkyldiarylphosphines, cycloalkyldiarylphosphines, dicycloalkylarylphosphines, tricycloalkyl-phosphines, triheterocyclylphosphines and trihetarylphosphines.
 33. The process according to claim 2, in which the reaction is effected in the presence of an added aprotic organic solvent.
 34. The process according to claim 2, wherein the reaction is effected at a temperature of not more than 80° C.
 35. The process according to claim 2, wherein the reaction is effected at a pressure of not more than 25 bar.
 36. The process according to claim 2, wherein the composition comprising the at least one unsaturated carboxylic acid of the formula (I) is an E/Z isomer mixture of the formula (I) comprising a 3-(E) acid of the formula (I-E) and a 3-(Z) acid of the formula (I-Z)

in which R¹ and R² have different definitions and R¹ has a higher priority according to IUPAC; and this E/Z isomer mixture of the formula (I), is subjected to an enrichment of one isomer.
 37. The processing according to claim 36, wherein the composition comprising the at least one unsaturated carboxylic acid of the formula (I) is an E/Z isomer mixture of the formula (I) comprising a 3-(E) acid of the formula (I-E) and a 3-(Z) acid of the formula (I-Z), in which, in addition, (1) the composition comprising the E/Z isomer mixture of the formula (1), in the presence of an alcohol and of a lipase enzyme, is subjected to an enzyme-catalyzed esterification, wherein the 3-(E) acid of the formula (I-E) is converted at least partly to a 3-(E) ester, so as to obtain a composition comprising the 3-(E) ester, unconverted 3-(E) acid of the formula (I-E) and unconverted 3-(Z) acid of the formula (I-Z); (2) the composition obtained in (1) is separated to obtain a composition depleted of 3-(E) acid of the formula (I-E) and enriched in 3-(Z) acid of the formula (I-Z), and to obtain a composition comprising the 3-(E) ester; (3) the composition obtained in (2) which is depleted of 3-(E) acid of the formula (I-E) and enriched in 3-(Z) acid of the formula (I-Z) is subjected to an isomerization to increase the content of 3-(E) acid of the formula (I-E); and (4) optionally, the 3-(E) ester obtained in (2) is cleaved to obtain the 3-(E) acid of the formula (I-E).
 38. The process according to claim 36, wherein the composition comprising the at least one unsaturated carboxylic acid of the formula (I) is an E/Z isomer mixture of the formula (I) comprising a 3-(E) acid of the formula (I-E) and a 3-(Z) acid of the formula (I-Z), in which, in addition, (i) the composition comprising the E/Z isomer mixture of the formula (I) is subjected to an esterification in the presence of an alcohol to obtain the 3-(E) ester and the 3-(Z) ester; (ii) the 3-(E) ester and the 3-(Z) ester obtained in (i) are subjected to a lipase-catalyzed enzymatic hydrolysis, wherein the lipase at least partly cleaves the 3-(E) ester to give the 3-(E) acid of the formula (I-E) to obtain a composition comprising the 3-(E) acid of the compound of the formula (I-E), unconverted 3-(E) ester and unconverted 3-(Z) ester; (iii) the composition obtained in (ii) is separated to obtain a composition comprising the 3-(E) acid of the compound of the formula (I-E) and to obtain a composition comprising unconverted 3-(E) ester and unconverted 3-(Z) ester; (iv) the composition which is obtained in (iii) and comprises unconverted 3-(E) ester and unconverted 3-(Z) ester is subjected to an ester cleavage to obtain a composition depleted of 3-(E) acid of the formula (I-E) or salt thereof and enriched in 3-(Z) acid of the formula (I-Z) or salt thereof; and (v) the composition which is obtained in (iv) and is depleted of 3-(E) acid of the formula (I-E) and enriched in 3-(Z) acid of the formula (I-Z) is subjected to an isomerization to increase the content of 3-(E) acid of the formula (I-E).
 39. The process according to claim 37, wherein the isomerization to increase the content of 3-(E) acid of the formula (I-E) is effected in the presence of an anhydride of an organic acid and a base.
 40. A process for preparing (−)-ambrox (VIII)

in which a1) a mixture of (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid and (3Z,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid obtainable by the process as defined in claim 2; b1) the mixture of (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid and (3Z,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid is subjected to a separation to obtain (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid; c1) the (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid is subjected to a reduction to obtain (3E,7E)-homofarnesol (VI); d1) the (3E,7E)-homofarnesol (VI) is subjected to a cyclization to obtain (−)-ambrox (VIII); or a2) a mixture of (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid and (3Z,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid obtainable by the process as defined in claim 2; b2) the mixture of (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid and (3Z,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid is subjected to a separation to obtain (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid; c2) the (3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienoic acid is subjected to a cyclization to obtain sclareolide (VII); d2) the sclareolide (VII) is subjected to a reduction to obtain (−)-ambrox (VIII). 